Which oil is recommended against a slightly slippery wet coupling? Currently is probably 10w-40 partly synthetic in the engine. Manufacturer recommendation is 10w-40 JASO MA or MA2. I can imagine 10w-50 MA2, like fully synthetic. Or is it true that fully synthetic oils (despite MA2-identification) allow the wet coupling to slide more easily than partially synthetic ones? What about the ester oils (with MA2)?