Hello, I got tired of reading through this thread, so if this has already been covered, please forgive me.
I was buying new tires for my 02 RX-300 AWD. The tire dude told me that I needed to replace all four tires at the same time. Why I asked.
Apparently, if the tire size from front to rear is more than a few 1/16ths of an inch, it causes excessive wear on the AWD transmission.
I bought the car with 30k on it, and the dealer put on two new tires, with the other two being at about 75%. I drove it that way for about 20k more before replacing the two "old" tires (this is when the tire dude educated me). The two replaced tires were at about 50%.
The tranny is a bit slow to shift when cold, but works fine otherwise.
I changed the Tranny Oil at 90k, and it was pretty brown in color. I intend on changing it at my scheduled engine oil change and re-evaluate.