neither Age or Miles are specific determining factors for the life of fork seals. Use and Abuse are. Many bikes that are well used but not abused can easily go 10yrs/100k miles b4 a Seal goes bad.I'm planning to change the fork oil and springs with progressive on my '01 800 Classic with 13,000 miles. The fork seals are not leaking but I was thinking of replacing the seals and/or dust caps while I have it all apart.
So, I'm asking from your guys' experience - is it likely the old seals will last until the next planned oil change (probably another 10,000 miles and maybe 5 years)? I usually tend to "over-maintain" my vehicles but if the seals are expected to last 20 years then replacing them would be silly.
That doesnt mean you shouldnt Change your fork oil every couple of years. You should 2yrs/20k is plenty reasonable use. Change is easy.
I've done mine twice now at 50k. The first change of factory stock oil was PUTRID. I had a left seal that started to weep and thought the same, Seal time.
I Drained the fluid, there is a drain plug bottom under the axle. the springs come rite out the top, Wiped them clean, Flushed the tubes several times with SeaFoam, lots of crap comes out.. Then replaced the fork oil with HD 20w FORK OIL. is clear as water new. Seal quit weeping and the handling is improved into the realm of "impressive.. astounding"!
If later you want to do a full tear down, well then you can. but to do it just cuz yor bored.. maybe you need a hobby? poncho