You know why I think the starter clutch problems is many, if not most times an "oil" problem? Because my starter works very well when it is hot or when it has been started once already that day. Its only when it is really cold or hasn't been started for a few days that you get the problem. And when it first came out of its years-long hibernation, all it would do is "whir." My mechanic thought the bike just needed to have the shit ridden out of it, which is also partially true. Which is also an additional argument that old gunk inside the engine case also had something to do with starter clutch slip and having the gunk burned out/changing the oil with high detergent oil accomplished virtually the same thing.
Remember, we are dealing with ancient machines here that have had decades for crud to build up in the engine cases. When I first started riding mine, the starter clutch slipped terribly, even when it was hot. Sometimes it would not start at all, even when it was hot. Now it never ever slips when it is hot. It never slips if it is cold but has been started, even if it ran only for a few seconds that day. And the first start of the day might involve two or three stabs on the button before the clutch engages. These are all compelling arguments that oil is the culprit.
With 20/50, it would still slip terribly, even though that grade supposedly had no friction inhibitors mainly I believe because the thick oil made engine turnover so hard. So my theory remains that you have to have the 5 weight lower viscocity number for the cold engine to be able to turn over on a cold morning. Sythetic oil naturally provides better lube, but most syn oils have friction inhibitors and have too little detergent effect because of the harm to catalytic converters. That leaves your motor oil choices very very few.
And you have to be content with very gradual improvement over time. My ancient Kaw has turned into be an extremely dependable and reliable machine without major surgery.