So I was driving to my friends house and my gs-r was shifting a little funny. I get stopped at a light and sit in neutral. The light goes green and I tried to put it into 1st and it wouldnt go, so i tried 2nd, 3rd, 4th, 5th, reverse. I had to call my dad : to come up there. I turned the car off, put it into first, and turned the car on, with the brakes applied and the clutch all the way in, the car feels like its trying to go. Anyway, I get the car home and we bring it to the shop. I already had told my dad it was probably the slave cylinder and he just disregarded me, thinking I have an adjustable clutch. The shop tells us its either the clutch master or the slave cylinder.
There was no visible leakage from either, and they say that it is a "hit and miss" fix. It's around 250 for one to be replaced, and 400 for both.(inc. labor) Is there any way to tell which one it is?? The guy said he would personally do the clutch master first, but I thought he may just be saying the opposite to rip us off.[paranoid]

Sorry for the length, but any help is much appreciated.