Drive shaft oil, I always change every year. Simply because the oil container is large enough to service the bike 5 times and I don't think open containers last 15 years if you were to do it once every 3 years. It's cheap insurrance. I also change my oil every year or 12K's.
Strictly follow the manual, especially when torqueing down the fill cap. I ignored it and snapped it off after a 1/4 turn to tight, resulting in a €40,- bill for just an fill cap (specially engineered to break without damaging the thread, but still.. 40 bucks)
...and a heart attack.