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After a 160 mile thrash up to Exmoor and back, I noticed evidence of oil expulsion from both breathers- I checked oil level and it was down the stick . Anyone got any suggestions ? Is this likely to be rings or valve guide seals?

Assuming your labyrinth 'valves' are present and correct in the rocker covers and the correct dipstick is in use my money would be on rings, though in that case I'd also expect a lot of 'mist' from the crankcase breather. The valve guides don't have seals (well mine don't) but they could be very worn. How much oil though? I used to have a catch bottle on the 350 when it was being run in speed hill climbs and it would always accumulate a little oil. The only time it was a significant amount was when I had it rebored and the place that did it got it wrong. That resulted in broken up rings and a lot of oil expulsion, which prompted the change to a '375'.

Think I have found the answer! On stripping the bike down to clean it after this ride, I found the large breather tube had been completely pinched under the seat. I have now redirected it but have not tested yet

jeromefack wrote:Think I have found the answer! On stripping the bike down to clean it after this ride, I found the large breather tube had been completely pinched under the seat. I have now redirected it but have not tested yet

That could do it!