I share your pain. Exact same happened to me a couple of months back. Think it depends on Sachs or LUK, mine had Sachs and so was replaced with Sachs for £700 all in.
No slipping now (touch wood) and I'm running with 322 lb/ft of torque. I can feel a slight grind/vibration feeling through the peddle, buy I think I'm just being paranoid as its all working fine.