Thanks guys,
I think that losing Castrol GP to Acteivo then losing the line altogether has been a wake up call for me, I use Morris non-detergent mineral 50 in the Manxman, the Velo Thruxton, the Velo MAC, the '55 Triumph T110 and the Duke Bevel 900ss in the Summer and Morris non-detergent mineral 40 in the winter, the BMW 900cc R75 uses Halfrauds Green Tin 20/50 all year round. The GB has been on Actievo 10/40 since purchase and the DR650SES went from Castrol GP to Actievo in the last 3 years of the 12 years I have had it. It looks like I will have to get used to Castrol Semi 10/40 or Halfrauds Semi 10/40 to replace the Actievo and hope for happy outcomes with the clutch. The remains of the Silkolene 10/40 can be used in the GB. By the way, I understood that it was the "long-chain" molecule structure of the oil that caused the clutch slip but trophydaves' post implies that it is an additive that does the deed, interesting.
Furry