Hi Phil, will scan a diagram for you later but the stripdown is very simple.
Remove the master cylinder.
Remove the brake lever.
Where the removed brake lever sat you will see the end of the brake piston.
Holding the rubber boot on is a simple circlip, remove this. I usually use a very small screwdriver for this.
With the rubber boot removed you will see a circlip, this seats in a groove in the bore of the master cylinder and holds the piston in.
To remove this you will need some circlip liers with long thin ends to slot into the holes in the ends of the circlip, when fitted compress the circlip and remove.
That's all there is to it, apart from the crusty dried up brake fluid that will be bunging everything up !