Its a tricky one. Mine started to slip one day when I sat on the biting points at lights on a steep hill. When I dropped the clutch it slipped like hell and just revved. Car was MY00 Classic with 100k on clock
Slipped again a few times on the way home and again in the morning, so I booked it in at my mates garage. Stopped slipping in the week up to getting the new one fitted.
My mate spend nearly all day doing it and looked well p'd off when I went to get it that night. I was met with " I am never doing one of those feckers again!"
Thing is he showed me my old one and told me it still had plenty life in it. Most likely overheated the clutch that day, but was defo not a need to do job. £400 pound bill though, and he dont charge me much for labour. Ouch.
Calculated risk though as it could go or actually be in the same state mine was and be good for a good bit longer.