If you have replaced fork seals, changed the fork oil, and also added gaiters so dried bugs on the forks can no longer mess up the seals - well, why change that oil every year or even two years?
When I did do it annually on my K75 (after all three above) what I drained looked exactly like what I added. My K100 now has a couple years with the same fork oil (again, after all three above) and just wondered if this is a little job I can safely skip. And for how long?
BTW, I've heard fork seals last basically forever when you use gaiters. If so, what other bad stuff can get in there?
As always, I'm sure I'll get some good advice from the knowledgeable people on this forum.