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Hi, what oil are you recommend available in the EU for 2002 Fs 650 after rebuild? viscosity?

I own 2 bergs 2007 and 1997. 07 is 650 and 97 is 501 wondering what parts available on both bikes are on big parts rods cranks pistons cylinders etc. both are mortarding and love them but both will be needing some maintaince I ride them both hard do track days any one can chime in thanks Edit...