A mechanic / stealership will want you to buy some servicing of course.
Me, I'm just a gen 3 user. Service manual doesn't have an interval for fork oil. I'd say wear in the forks won't get contaminated like engine oil, buy it does wear slowly. So, inspect and watch out for noise or non smooth action. I had a fork leak, cleaned the seal with a home-made sealsaver, and still running fine after 80'000km.
But I'm thinking about it... Why? Only because I expect an unrecoverable leak at some point. Fact is, you will eventually end up in the shop for a fork seals replacement (perhaps even the bushings), and they may change the oil then. So I would wait until then.
The oil is not to blame, the dust and dirt may fail the seal and that when you need to do something. I did the sealsaver trick 30000km ago. No issues.
I would recommend neoprene fork sleeves though. That is very effective against dust/dirt.
Last edited by dddd; 07-17-2019 at 06:03 AM.