it sounds as though you have got air in the clutch hydraulic system.
I am not sure if the 400 has got the same plastic clutch parts as the later 45\ZS, but it is pretty much a sealed system - there is a way to bleed it, but it is not that easy. (have s search on here or on xpf for a thread by sheddist)
Mine did the same thing, but had popped a sseal, so once the clutch went to the floor, no more clutch. For yours to slip it means that you are wearing your clutch as it has not re-engaged properly.
I am not sure if the 400 has got the same plastic clutch parts as the later 45\ZS, but it is pretty much a sealed system - there is a way to bleed it, but it is not that easy. (have s search on here or on xpf for a thread by sheddist)
Mine did the same thing, but had popped a sseal, so once the clutch went to the floor, no more clutch. For yours to slip it means that you are wearing your clutch as it has not re-engaged properly.