Are you replacing the fuel pump by it self or as an assembly with the sender? By "cluster" the mechanic means "instrument cluster." Maybe post where you live and someone might be able to suggest a mechanic.

I am not replacing anything. I am trying to determine the root cause of the fault. I live in San Diego.

You can read the Ω from the sender unit. If you look at the range of values. You can back probe to read while plugged in.

Good question about the fuel pump. Was the pump assembly replaced with the sender unit with the pump or just the pump.

@andrewwynn do you happen to have a source/link/ part number for the O ring?

I’m fairly confident that I have a problem with my siphon pump now. Car seems to run fine with the fuel level always kept over a half tank and running it down it 1/4 to 1/8 saw it cut out while driving along.

I’m hoping it’s just an O ring that needs replacing as per the above example too.

Finally got around to pulling my siphon pump today. Looks like this:

https://i.ibb.co/2jC5S3w/IMG-2845.jpg

Am I right in thinking this look as it should be right now? So the only thing I should need to do is put in a zip tie?

Looks like you beat the o-ring to expose itself. Yep put in ziptie. You can just slightly see it's starting to tilt toward letting o-ring come out.

It's "next level" test but I put the unit mostly in and run the fuel pump to make sure the bottom connection also not leaking it has no actual gasket.

I put in an o-ring on the bottom connection but don't bother if it doesn't leak it's a fair amount of work.

If the lower connection is leaking then a piece of glue lined heat shrink works nicely.

That's a great tip I also had success with hose clamp. It's a moronic design with plastic to plastic connection no seal. Both our e53 were leaking there at about 130,000 miles and 15-16 years old. The upper o-ring was much worse sprayed so much the siphon jet stopped working at about 1/4 and 3/8 of a tank.