Or...possibly glue some more rubber to the bottom of the stopper so it rests where you need it to be?

There is a low mileage '97 M119 motor for sale locally. At this point it would probably be just as feasible to swap that in... :D

New symptom in this epic saga:

The car has been doing this for a while now, but I just put together that it's a symptom & not just in my head: The car will start & run right now as long as you keep the rev's up with the throttle. However, after running for a little bit whilst I'm diagnosing things/moving the car out of the garage/whatever, and then letting the car sit for 20min-1hr, the car won't start. When you first crank the key, it will catch for a sec and then nothing. I'm assuming that that's the cold start valve pushing fuel in. After that you can crank away & get nothing. Let it sit for a while and it'll start up again.

Does this symptom ring any bells for anyone?