Same lock problem with my '92 945T. The key will only go in part way.

I finally found a lock assembly in a wreck with a key, but unfortunately it was broken at the inside end. I took it anyway to take the lock apart and see if I could fix mine. The key presses up on about a dozen little metal tabs on both sides of the lock cylinder. I think the problem is likely to be a dissimilar metal corrosion problem causing deposits to form from the pot metal lock cylinder and dust and road grime.

It looks like if you remove your lock assembly (the one I removed was held from the inside with a zip-tie that I cut), I think you could remove all the little tabs, keeping careful track of the order and which side of the lock cylinder they came from, then lube with graphite and reassemble. I haven't had time to tackle this yet on my car, though.

It's worth a shot-- buying a new lock assembly is probably going to set you back a chunk of change!

Good luck!