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As you know these engines don't take an overheat, even a brief one , very well.

you greatly increased the risk of a head gasket /warped head b driving your car the quarter to half mile home while in the red...

Before you replace any parts you need to test for head failure AND find the source of your leak.. BTW - a pressure test at 9psi does nothing...the M54 cooling system runs at 18-20psi...

I would do the following:

• compression test
• swab each cylinder for coolant...run the car up to temp, shut it off let it sit overnight, pull plugs and swab each cylinder
• Maybe get a UV coolant test kit - dye, UV light, glasses - you might be able to borrow at Autozone.

Right now, I think you have an air pocket in the cooling system..keep bleeding...then do the steps above..

 

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I forgot to mention I re-did that test and pushed it up to 18psi. The gauge immediately starts decreasing, but slows as it gets closer to around the 9psi mark, where it will then hold around the 9-10psi mark.

It's hard to say if I'm getting a reliable reading, but I tried it quite a few times and got this same result.

well you definitely have a leak..it should hold 18psi

 

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what brand was the water pump that failed?

The failed water pump does not explain the loss of coolant and apparent coolant in cylinders..

 

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Saleri.

Yeah it pretty much does since the water pump failed and the car overheated. Probably warped the head and/or blew the head gasket, so it was burning coolant. One of the first things I mentioned was that I could see white smoke in the exhaust, so I think this is the root cause of all the issues I encountered

Sorry to hear...I think I have a newer Saleri water pump in one of my cars...Hmmmm