Here is a very good start to finish video (which does extend to a full rebuild). For a simple oil change just jump the bits that do not apply.
Interesting to note that many fork seals are sold with dust seals as well. I'm thinking of replacing the dust seals after cleaning out the retainer cavity and changing the fluid. Does anyone have any experience with aftermarket dust seals? All Balls?

Changed my fork oil out in my 2015 650 XT a couple of months ago and it was the color of mud and thick. May of had some water intrusion, I'm not sure. The new fluid was clear with a yellow tint. I will probably change it out every couple of years from now on. Its easy enough and cheap.

I have some Cogent dampers/intimators on the way and will use those charts to ensure I do buy a good 5wt fork oil. The only thing is that it comes in 1 litre bottles, I need 500mls for each leg, and I would like to put a little in first and pump out any old oil in the bottom.
I may use Rolex's idea in Post #3 and pump a little ATF through as I have a part bottle on the shelf. Did you ever learn the actual viscosity of ATF Rolex? 5 or 10 maybe, it is quite thin.

I changed out the fork oil on my 05 650 every year(12-13K). It was always the dirtiest stuff ever drained from anything I ever worked on. It was an accumulation of dirt, dust, bugs and water(It rains a lot in Washington) .
At 100K Rancho fork boots were installed(Greywolf always was recommending them). Fluid change at 110K. Oil looked good. Clean enough that it could have been reused(Wasn't). Checked again at 122K with the same results. Do yourself a favor and install some. 30 min. job.

I'd say you're right on the money. ATF was the spec fork oil on my old V65 Sabres and a lot of people experimenting with different oils determined ATF to be 7.5 weight.

Thanks. Gogent specify 5 wt for their Damper catridges so I'd better follow that, but I will definitely flush with ATF.

I had been told about 30 years ago ATF was equal to 10w fork oil and I have always worked on that theory. ???

I was told to use it because it was more stable when it got hot than fork oil. ???

I have no idea if my information is correct.

Now of course oils have changed in that 30 years but I have not kept up with the times.

To this point I have been happy with my use of ATF, if I was ever unhappy with the performance on a bike I would start to experiment.

I will ask the guys at my work if they are able to test some oils for me and see what numbers they come up with.

ATF seems a good idea as the stress and heat produced by being pumped through chambers/orifices is surely similar between auto transmissions and motorcycle forks. Gogent clearly emphasise the need for 5wt oil for their units to work as designed.

Does Cogent specify a particular brand of oil? Ricor does with their cartridge emulators.

Reason being hydraulic oil is not regulated as to weight like motor oil. One manufacturer's 5wt is another's 10 for example. The chart posted by Big Boy lists oil by centistokes(sp) that is the only reliable guide to viscosity.

The reason that emulators require very light oil is to negate the damper rod ports. it's "thin" enough to flow through the holes effectively bypassing them. The cartridges will be configured (ports and shim stacks) for a specific oil normally.

From their installation instructions:
"Your Cogent DDC was calibrated to use Golden Spectro Cartridge Fork Fluid 85/150 (5 wt) which is a synthetic blend suspension fluid made in the USA......"
Unfortunately that fluid does not seem to be available here so I will need to look at those charts carefully for an alternative.