Oh my gosh. You sound like your in the exact situation i was in a few months ago!

on my 92 300D 2.5

i replaced the transmission at dealer for 4 grand
Then new tires mxv4 for about 450
then new motor mounts, tranny mounts, R12, paint job etc.

Then #4 cylinder was acting up and my car was missing all the time, I took it to dealer they said I have low compresssion in one cylinder and wants 8500.00 plus extra parts to get it fixed. So a total of 10 grand.