Yikes! You have a fog of problems that you somehow need to sift through. A few comments:

1) It has to have some sort of crankcase ventilation valve - otherwise, the roads of America would be strewn with BMW X5 engines that have launched their dipsticks through their hoods. Find someone who understands these engines, and have them look at it.

2) A complete engine rebuild at 86K miles, which is what the dealer is recommending, unless the engine has been terribly abused or neglected, is nuts. Again, find a trustworthy independent BMW mechanic and have them look at it.

3) Those compression numbers are weird. I've never done a compression test on my X5, but on my Porsche 968, if they drop below 170, something is wrong. The ideal gas law applies to an X5 engine the same way it applies to my Porsche's engine, so something sounds goofy about those numbers, at least to me.

4) The fact that it doesn't start if you let it sit for a few days indicates you have a parasitic current leak. This is a whole separate issue from your engine problems. I just went through a long period of troubleshooting a similar problem with my X5, and I came up with a solution. I can help you with this problem, but to be honest, it pales in comparison to what you've got going with your engine at the moment. But to keep it from continuing to die, I'd recommend that you start with the fuse block in the right rear luggage compartment, pull the fuses one by one, and place the leads of an ammeter across the connectors of each fuse after you've pulled it. Anything over about 30 mA is too much current flow. When you've found the one that is drawing a large amount of current (I'm guessing you have something north of 200 mA), check what the fuse goes to, and if you can, remove it when you're not driving the car. If you don't find the offending fuse in this fuse box, do the same exercise in the fuse block behind the panel inside the glove box. There are a lot more fuses there, so this is more of a pain, and you have to remove, or at least unhinge, the glove box door to gain access to the fuses. Good luck!

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT