Just a question, why do you want to go for the 3000GT SL anyway? They are extremely slow! The only 3000GT worth getting is the 3000GT VR4 which moves decently fast and has AWD, however you do not want a 3000GT VR4 with 120k mi unless you are willing to spend money on the tranny.
I'd suggest you find a forum for 3000GT owners and ask them, they will tell you any problems that are common to 3000GT of your vintage and mileage.
Unless you really want to have a 3000GT for personal reasons <ie: always wanted one since you were a young child or you have some sentimental reasons for one> then buy it or search around for a better deal for a 3000GT...maybe you can find a VR4.
Else, you can do better for a sporty car. The base 3000GT are extremely heavy (pushing 3500lbs) and pretty slow with a 200hp engine. The VR4 is twin turbo and makes 300hp and is AWD. However their trannies are known for their weakness. A base 3000GT is not a fun car to drive, atleast not to me.
Did you test drive the car? Don't go buying it because its relativly rare and you want one cause it looks cool and is a sports car. The VR4 is a sports car...not the run-of-the-mill 3000GT.
I'm not flaming you, just trying to warn you before you get into something that you can't get out of. Think sensibly, don't fall into the 'getting a rare sports car' thing like many others, who later realize it didn't meet up to their expectations and/or they can't afford it.