The oils I've used in the X Wedge are Morris Race 20w50, Motul 7100 20w50, Valvolene VR1 20w50, Amsoil V Twin 20w50, and the oil I am currently using is Fuchs Titan Race Pro R 20W-50 Ester Fully Synthetic which is a top quality oil for not too extreme a price.
Unless you send oil samples away for testing and strip the engine down and measure and inspect everything how do you know what's going on with each oil.
The only thing I can say is that the mineral and synthetic oil wet sump to the same degree and that the mineral oils appear to not flow so well at cold temperatures.
Personally I think the problems with the engine come with how well S@S have manufactured it in the first place with some variable tolerances and material quality rather than the oil used.
