Shimano freehub bodies generally aren’t too bad to remove off the hub.
If you do that, you can gently remove the rubber seal, and then quite efficiently flush the f/h body. Aiming a stream of WD-40 or similar between the shell and the bearing cup while turning it can do wonders.
Disassembling Shimano f/h isn’t too bad. There is a special tool, but it’s quite easy to improvise around it. I’ve simply used a wide enough file, stuck in a vise to engage the notches in the bearing cup. It unscrews counter-clockwise.