Sounds like the clutch isnt disengaging fully, because it shouldnt crunch when engaging reverse, if you select 2nd gear before engaging reverse and it still grinds then it's as definetly not disengaging, always engage reverse slow then if it does ever grind your not using much force to put it in with.
Possible causes is that they may not have bled the slave cylinder properly, really you need to used a power bleeder to bleed it properly, you can buy then from halfords around £16 and it connects to the brake res and forces brake fluid under air pressure supplied by your wheel or spare wheel.
You then just connect a brake bleeding hose to the clutch slave nipple and open it watch for air bubbles and one it flows clear tighten the slave nipple back up, and disconect the bleeder from the brake res, i've not used one yet but i'd think when you take it off brake fluid will overflow from the res and go everywhere so get ready with some coths, and you clutch should now work normal.
It may be the clutch but before replacing clutch master cylinder and or having the box taken off to see if theres a problem with the clutch, try bleeding the thing first.
1999 mk4 golf 1.8T agu, current mods - standard panal filter / drilled air box, custom code stage 1 remap, with 4 bar fuel pressure reg, new 288mm brake discs with mintex pads.
Future mods - turbo back jettex exhaust, silicon turbo intake pipe, forge split-r valve, lowering kit, & them some nice 18 inch wheels with 225 width tyres.