you need some runner guides. One at the front and two at the back. Pull pin out under front of seat (springy clip). slide seat out rearwards. You will see two plastic parts, one on each side of rear, replace these, also a different shaped one at the front where the seat locates. Have a look on ebay, they are quite cheap.
http://www.ebay.co.uk/itm/VW-GOLF-MK1-MK2-MK3-GTI-SEAT-CLIP-GUIDE-C66-/190509681032?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2c5b430988Tierod69's stuff is top notch. Have these exact clips myself and fit perfect.