I am unaware of any deficiency with clutch springs for that model. I can assure you that if you continue to ride it with it slipping you
will need a new set of clutch disc, and that still will not fix the problem.
Questions: Did the bike start slipping after you changed back to conventional oil?
You are saying that the longer you ride the worse it gets, is this only when you try to accelerate? If you come to a complete
stop and take off again, is it slipping in all gears, or only after you have gotten to 5th.
Has anyone ever been into the clutch before?