This is what happened to mine too. Car is on 80K now, chipped (+ KO3S) since about 50K. Clutch started slipping every now and again. My flywheel ended up knackered so I ended up buying the Spec Stage 3 clutch from JBS. SEAT wanted £650 for a new clutch/flywheel assembly. Couldn't justify buying it as I knew it would just slip again (see sig below for torque car is producing). It was ok most of the time when on low boost (around 250lb ft) and didn't slip but the clutch couldn't handle the high boost setting. The Spec clutch cost an extra £150 over the OE kit but I can't fault it. Very stock feel, lovely to use and it GRIPS!!! I looked at a couple of the more popular upgrades (Sachs etc) but the torque rating they gave didn't fill me with confidence, although the price for these were a lot cheaper than the Spec clutch. I may have paid over the odds for the Spec clutch as I was in a hurry for it (car was off the road for a month of Xmas) but JBS may be able to reduce the cost, depending on how many they order.
Hope this helps.
Damo