I have a clutch slip problem on my '98 Wr400. It occurs only in top gear, but at all rev speeds. I have fitted a complete new clutch with H/D springs and boths sets of plates (Yam stock) hoping to rectify the problem, but it remains. I thought the clutch I removed looked OK. It looks like it was an uprated clutch as it has dimples on the steel plates, unlike the new standard yamaha clutch I have now fitted. Someone mentioned it could be the oil type, and suggested going to mineral oil might solve it. I am currently using semi-synthetic oil (which has been recommended to me generally as it is an old bike), against synthetic oil, as recommended by Yamaha in the workshop manual. Or should I try going back to synthetic oil? Or none of the above? if anyone can help I would be grateful. All the best, cheers, Red.