I think this is good advice, so I actually ordered both. Hopefully, when I get back in there, the cause of the leak will be apparent. I'm fearing not being able to tell what the cause is and then having to resort to a trial and error sort of thing.

I'll post new pics when I get back in there.

Most mechanics and service advisors don't even know this, but any time a seal is replaced on a rotating shaft on a used engine, it will never work to do its job sealing unless the shaft surface has been re-surfaced to its original, like new diameter with a repair sleeve. There are no exceptions to this rule.
Some people say, just treat the surface with some light sand paper and that's all incorrect.

A diagnostic step that should be performed is installing a water-manometer to the oil dipstick and determine if blow-by pressure inside the crank case is above factory specification, and if it is, installing a replacement seal and sleeve won't work either as crankcase pressure is working against the sealing surfaces.

There is a cost-benefit comparison to be performed to replace a leaking rear main, and all low cost alternatives should be explored and tested.

In the hydraulic rebuilding industry, any time a cylinder rebuild is performed the cylinder will be re-chromed along with a full seal kit installed. Only installing new seals will never last passed the warranty period.

Here's what I do when I see a leaking rear main;
Add AT-205 re-seal to the engine oil. Add AT-205 into a spray bottle, soak down in between the engine and transmission so the product can contact the outside of the seal face.

When I 'am in there' on a used engine doing a clutch job with the transmission removed, I clean the rear main seal with brake clean, and then give a liberal application to the seal with the spray container of AT-205, paired with adding into the engine oil.

All you need to do is contact a manufacturer in the heavy equipment seal industry. They will need the new shaft diameter specification, width and a sample of the oil seal. A custom repair sleeve can be made and sent out.
I have ordered these before when repairing old fork-lift truck seals where there are no parts availability. Once you replace the seal and repair sleeve at the same time, and the crank case pressure is not over the limit, there will be no leaks. be sure to follow correct procedure such as use assembly grease on the parts.

Glad I've been real lucky then as I change them anytime I do a clutch or engineer/trans separation. No issues with continued leaking... Yet. *Fingers crossed*

It's possible. If previous maintenance is legit and used only synthetic with proper change intervals, and under 2000 engine hours / 100,000KM there may be little to no wear. The problem is the seal and shaft will wear at the same rate, the new seal cant deform to the larger gap created, without being able to overcome the crankcase pressure. Crankcase pressure will be highest on a cold engine and at engine idle. The less load on an engine, the less the piston rings will seal allowing exhaust gasses to pass the rings into the oil sump.

As well, if the seal is not currently leaking and a new one was to be installed as preventative 'while you are in there' maintenance, there is less a chance, but then you can restore the rubber with a conditioner added into the oil or sprayed on the outside, so then there's more of a diminishing return to re and the rear main, and risk a bad seal alignment or damaging the shaft surface.

How do you measure the drip rate ?

I had a very picky customer complain of a single drip of oil per night when the equipment was parked.
Used a white oil absorbent pad, and idled the engine and measured one to two drop per hour. The rear main seal had been replaced almost a year ago, by another mechanic in my shop, using OEM parts and factory manual procedures and tools.

Deciding what is a reasonable rate of oil drip vs the cost to re and re and warranty your shop work. Especially a 30 hour job.

I'm curious, are you doing this with a full lift system or jack stands on your back? This job requires a complete disassembly of the drive train? Trans removal? Front subframe removal to get to the oilpan n rear seal?

I shoot for completely dry but will tolerate any seepage that doesn't leave the engine/trans "wet."

I have a 4-post lift - best tool investment I ever made because I'm getting too old to do this kind of stuff on my back! About 10 years ago, I pulled the trans from my wife's e46 convertible to fix the infamous 'no reverse' problem using only jackstands - never again.

From memory for the rms and oil pan:

1) mufflers come off
2) center exhaust comes off
3) heat shields come off
4) F & R driveshafts come off
6) trans comes out
7) clutch & flywheel comes off

now you have access to the rear main seal

keep going for the oil pan...

8) stiffening plate comes off
9) front axles comes off
10) front sway bar comes off
11) front subframe comes off (I left the ps rack attached and disconnected hoses)
12) front diff comes off
13) dipstick and tube comes off
14) ps pump comes off (unbolted and pushed aside if you're not changing hoses)

now you can drop the oil pan

I disagree with this sentiment as I've probably replaced over 100 seals on rotating shafts that have done just fine - crankshafts, camshaft end seals, differentials, transmissions, axles, etc. Keep in mind, these seals aren't under any kind of pressure. Most are there to prevent lubricants from just sloshing out the end of the shaft as the lubricant is agitated.

In a pressurized hydraulic system, you're talking about a completely different animal where the forces can be quite staggering. Yes, those seals and their mating surfaces need to be perfect.

I don't have a lift (wish I did), so I do this on jack stands - with the car as high as I can get it - with plenty of safety back-ups (wheels under car, jacks, blocks of wood, etc.)

A harbor-freight transmission trolly jack is a huge help in this job. well worth the price..

I take the exhaust off in one piece at the down-pipe.. I support it at muffler and lower it carefully..It's heavy.

I don't always remove driveshaft. You can sometimes disconnect just the front end and center support and move it out of way. Try that first.

Get the correct e-torx sockets (E10,E12, & E14) to remove bell-housing bolts and make sure each one sits square before loosening. Attack as many bolts from top of engine as you can. They all strip very easily. An E-12/E14 (10-12 inch long) combo box wrench is a also a good tool to have.