RE: After-run oil question
Tim,
The standard Castrol Syntec (not German Castrol) is primarily made up of what the lubricants industry refers to as Group III basestocks, Group III basestocks are hydrocracked from petroluem basestocks and are generally recognized as "synthetics" by the lubricant industry. Teh German Castrol Syntec, currently only available here in the US in 0W-30 weight, is an Ester basestock. These basestocks are a "Group V" basestock and are a step above the PAO's which are "Group IV". PAO's (Gp IV) and Esters (Gp V) are "synthetic".
Any Group IV or V type oil should be just fine in your YS engine. Redline motor oils are mostly Group V as well, Mobil 1 has traditionally been Gp IV and I have no idea what Amsoil is.