I REALLY wasn't trolling for another oil thread. Use whatever oil wiggles your wagger. I've used synthetic for many years, brands including Mobil 1, (before the fuel conserving crap) Motul, Esso (Exxon), Spectro, Canadian Tire (made by Esso if you care), and now Amsoil motorcycle specific.
I have had no issues with seals leaking (excepting the 400F head gasket leak, but it leaked with petro oil as well). O have no explanation for it but every bike I've switched to full synthetic has run better; smoother idle in particular. Except when I broke a ring and blew a lot of smoke into an engine, the inside of the motors using synthetic look shiny new when opened rather than the gummy varnished look of petro oil engines.