I've a mk2 16 valver with nearly 125k on the clock and sometimes when accelerating hard in 3rd and 4th, the clutch appears to be slipping, i.e. the engine revs but I don't actually go make any progress (very similar to driving on snow). I can put her in 5th at 25mph, put but foot down and she pulls fine. Also there is no judder. 1st and 2nd appear to be fine, this has only started happening since yesterday and have driven about 18 miles with this happening.
Could my clutch be on the way out - if it was, I'd expect it to slip in every gear, not just 3rd and 4th.
Anybody got and ideas/suggestion please......??

Thanks - Andy...