Leaky cylinder head base gaskets were much more prevalent on the M750's and M600's but occassionally an M900 would get one.
1999 marked the year of the return of the 'V' stamped cylinder heads which would have the true 900 cams and larger valves so no worries there.
1999 also had the 3-phase charging system (much improved over the single phase) so that's good
1999 was the last year of the carburetors. (good or bad depends on your ability to tinker and if the bike has sat for a long time unused...)
1999 still had the old-style slave cylinder so it's ~ok~ until it leaks then just replace it w/an aftermarket one...
1999 M900's got adjustable front forks and a Showa rear shock *unless* it's an M900Dark then it got crap for suspension all the way around.
Old suspension still (until 2001) but it can be made to work good. 2002 & up is better but not substantially.
1999 *may* still have the self-retracting -or- suicide side stand bolt on it. REPLACE OR GRIND THE TIP OFF AT ONCE!
Overall, I'd rate that model a solid 8.5 out of 10. Pretty damn desirable.
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