Since I've owned my bike the rear brake peddle has been too high for me so it only gets used for hill starts.
I initially tried to adjust it but it is either just very tight or completely seized. I was then warned not to try too hard as they are apparently prone to breaking.

Is there a way of getting it away from the bike so I could get the whole adjuster section on the bench to work on it with heat etc.
So what I guess I'm asking is will the arm come out of the master cylinder without harming it or pulling the seals out?

I have done some searching around and although I couldn't find anything 990 SD specific I have seen some general rear master rebuild guides and it seems like to remove the "ram" you need to first remove the retaining circlip. This means there's a very good chance the piston will pop out and thus the job becomes a fluid flush too.

It can wait until next year I think as I have now taken the bike off the road for this season but I still need it to working for it's up coming MOT in a few weeks.

Next spring it'll be getting a full brakes service, new rear pads and fluid flush so that'll be the perfect time to tackle this job.