On the topic of Castrol R V's Castrol M. Just prior to VMX titles this year I was after some Catrol R40 which is what I used to run in my Husky back in the late 70's, my local auto parts store wasn't able to get any R40 and gave me the phone number for Castrol tech support. I ended up talking with one of the people there who was quite happy to explain things. Castrol R was originally formulated for use in 4 T engines running on petrol, were as Castrol M has been specifically formulated to be mixed with Methanol and run in 2T engines. I happened to still have about 20L of M in my shed, and the Castrol guy said it even though it wwas designed for use with methanol, it would still mix ok with petrol, so long story short, I am now using up my stock of Castrol M.
CJ