the owner of the 87 GT I'm looking to buy says the transmission has a bearing whine. what causes this and is it expense/important to fix?

 

I'd actually want to know more about the owners knowledge on T5's. On a good day, they are quite a bit noisier than most other cars. It could potentially be fine.

Also try to find out when it makes the noise. In all forward gears, in neutral or any gear and rolling.