I would think twice about going full synthetic. My 98 bike suffers clutch slip on the stuff. Fine on semi-synthetic or straight dinosaur oil.
I use any JASO-MA 10w-40 with no ill effects. Regular changing is probably the most important thing. I'm not exactly disagreeing with you Hoonicorn, just my experience on an older bike.
OP, you mentioned an engine flush....... May I suggest you just use a cheap bike oil rather than some kind of additive to achieve this. Warm engine, drop oil, replace with cheapo and heat the oil again, drop, change filter and fill up again. It will still shift a lot of spooge but not impact on hard seals and the like.
I started to do this with older engines after seeing some very mixed results from additives.
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