I did mine recently. I used to have an F800GS and the rear would go dark (really dark) every year and from what I've read online it was pretty normal. The front would get darker, but not like the rear. So I did a complete flush when I did my 6k mile service with a regular off the shelf DOT 4 fluid. It took about 30 mins and I put the whole qt of fluid through the system. Time will tell if it's going to be like my GS or if they've improved the reservoir seals finally, def a Brembo thing because it didn't matter what brand fluid I used.