The fork oil isn't on the maintenance chart. Some have replaces it. I just replaced my fork seals last summer. And if I was going to go through the trouble of removing them and changing the oil, I would atleast change the seals out. And if you were thinking of upgrading the springs, I would do that at the same time.I have a 2008 M109R, 3rd owner. Seriously doubt fork oil has ever been changed. Has anyone done this without the special tools shown in the service manual? Any suggestions for doing it yourself?
That is an approach that I wouldn't take. I have been riding motorcycles for 5 decades as well. I have changed fork oil on all of the used bikes I have picked up over the years. Oftentimes going to a heavier weight. I can tell you that the stuff coming out has at least some noticeable degradation by way of gray sludge/suspended particulate. I have also had instances where the oil volume in the fork tubes was insufficient or not evenly matched.I've been riding motorcycles for 56 years and have changed the fork oil in one of my bikes because I wanted to, not because I thought I needed to.