Putoline 75W 90 fully synth here.
As an aside, on a trip up the Dalton to prudhoe bay last year out of a group of GS's two had had FD rebuilds and
both had had 140's put in and both leaked, mine (53k miles and no rebuild yet) and the others with 90's were fine.
One of the 140's bikes FD which has been put back onto 90's is still leaking and will need to be stripped again.
I make no comment on the suitability or otherwise of the different grades of oil i am just reporting my experience.
Mmm I think all that proves Tony, is that perhaps the rebuilds weren't as good as they might have been. Doubt the grade of oil had much to do with it but ya never know.
I see what you are saying about the grade and i agree but I'm confident the rebuilds were of an excellent quality as i have had rebuilds done by the same person on mine and other's bikes and they have been fine
but, i have always refilled them with 75W90 oil. These had had the 140's put in. As i said, just a comment really. Many others will have used 140's for 1000's of miles without a problem. That's the way of these things