after replacing all the seals, timing belt, ccv hoses, the car runs great, and 2 days later, what is this new thing?

1991 945 turbo 225k. after driving about 45 min both highway and residential speeds, i stop at the post office to get some stamps. when i come back out, the car will not move when shifted into drive, 1, or 2. engine revs normally, trans seems stuck and wheels don't move. like you are stuck on a curb, only you're not. reverse works, so i try rolling back then hitting it in drive. nothing. finally, after sitting perplexed for a half hour, i try it again and it does the same thing, then finally gets over the "hump" and starts to drive. next time i park and come back, same thing, and reverse begins to have trouble moving. no real grinding, just the inability to move. tranny works fine when it gets over this invisible barrier, has no problem going from gear to gear, but after parking and restarting, it keeps happening. i don't really know how else to explain the feeling, other than it is like trying to move the car while up against a wall, then it finally decides to move the wall slowly, then the wall is gone, but not without quite a bit of effort. oh, yeah, and it spits motor oil out from underneath the motor like crazy while doing it. we're talking a stream. i don't know if the two are related, just an observation. trans oil is fine and has no burnt smell. i also now get an occasional huge clunk from the rear when accelerating from a rolling idle. what is going on with this beast? none of this happened before. it is really cold here (nj) right now, if that has any relevance.

oil light is on even though there is plenty of oil. does the oil light also indicate too much crankcase pressure? even though i replaced all the ccv parts, there still seems to be inordinate pressure, and previously the light only came on when the oil level was low. this is getting annoying, i thought i had it all under control. ahh, hubris. help. thanks.
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'75 164e(?), '87 240gl(350K), '84 240 gl(233K), '91 940se(225k+?)