Good news, it can be replaced rather easily. Just go to this site and select you model, the seat foam on the bottom is all you need it was $24 but when I ordered they said it was superceded by a newer part which is $67. But on the bright side you'll notice the difference, the foam is from Germany and nicer than the POS mexican foam that was stock.
Installation isn't that hard. To do it easily you'll have to cut the fabric in two places under the plastic bracket on the door side of the seat, otherwise you'll have to take the whole seat apart and off the track (not recommended). After you cut it pull the plastic strip from underneath the back of the seat and loosen the piping that holds the cover around the frame. Pull the seat cover over the foam to the center console and use a needle nose to pull the metal rods out of the old foam. Put the new foam in place and have fun getting the rods back in the hooks on the foam. Then tuck the piping back around the bottom of the frame and put the plastis strip back under the back of the seat in the slot and replace the plastic cover on the door side of the seat.
sounds easier if you just buy a new or used seat. maybe a junkyard or auto parts recycler. i tried to get gti black leather interior from a vw dealer.... or should i say tried to order it through them and they said i would have to order each part to build a seat. so i would not recommend that!
veedub you're from Bath, right. I went to L&T (VW Graveyard for those outside the LV) and they wanted $125 for a complete seat, which didn't guarantee that the used seat's foam was shot, so I went for the new foam. Then I dissected my seat.
lenny overcharges for alot of things.... but i know him pretty well and i guess get some good prices. i actually picked up some recaros for my 91 jetta project from him. they were in perfect condition minus a small wear mark on the outside bolster of the drivers seat for 50 for the pair.