most likely the box, easy to swap out on the mk3's and 4's, ive just done my mk5, box's start at £120 at the local breakers around my way, i got one out my self for £30 but had no guarentee! that is for a 1800i box for an rst you will be looking alot more unless your V lucky, id expect around £250 for a second hand box, just guessing mind i could be way off,

Dont be put off over a box change, knock the guy down on price and swap the box!!! its not a big job, the box is on a cradle so you just unplug sensors, remove clutch cable, undo bell housing bolts, drop out ns suspension from the top mount and wishbone, comes out in one piece so saves messing about, and drop the cradle, had 1 out in 25 mins at the scrappy, so is an easy enough job!!!

plus get one hell of a discount on the car

if too much for you to do, let me no asking price and location as im allways after the easy fix's for a bit of pocket change!!