Ya, well did some more searching and reading and I will take the advice and change all 4 tires.
My question is: assuming the car did about 4K-6K miles on tires that were not exactly equal - how can I tell if any damage was done? I took the car to a complete check out and everything turned out perfect, of-course...
I see that different tires put "stress" on the central diff - but at what point is real "damage" done? If I get them changed quickly - I can assume that I will have no diff problems for a long period?
The car has about 24,000 miles and I guess that more than half were done on original setup. like I said - I found nothing wrong with the car. (missed anything?)