Is there an online guide with pics or is it just a case of unscrew everything and then put it all back together?

I assume this is the best course of action for a non-moving piston.

Also since the non moving piston is on the side without cap access how do I get it out?! Holding the moving side back with an allen key and pressing the lever it still refuses to move. It was a very muddy ride.

Could I soak the whole caliper in brake fluid? Or would this eat the anodising off?

keppoch.

have a look here

Hope Mono Caliper Overhaul (Mini/Trials/M4/V2/M6)

Great guide, thanks.

keppoch.

Do your utmost to get the non moving piston moving before you dismantle the system – its far easier. Hold the moving piston in and pump the lever – I use a couple of cone spanners that fit across the middle of the calliper where the disc would run – they catch on the edges of the slot in the calliper so remain in the middle – pad in the moving side and no pad in the non moving side

I agree with TandemJeremy on this…

Just fitted and bled some Mono M4s (gold caps) and took the chance to pump the pistons almost out, and give them a clean up with ear-buds and DOT fluid.

Gets rid of any crap, re-“lubes” the seals and stop them sticking…

Mmmm slidey slidey pistons : )