I just rebuiilt one of those MC for my Inno. Be very careful when taking it apart, if it feels stuck in any way NEVER EVER TWIST OR ROTATE it. The two pistons are connected by a metal loop which is not replaceable. If it does not move just leave it to soak in penetrating oil try again, if not soak some more and leave it.
You can buy all the seals in a kit from MiniSpares http://minispares.co...px|Back to shop
Here's the extract from the parts book showing the exploded diagram of the MC. you will need some long narrow circlip pliers to get to them and be careful not to damage or score the bore of the MC as you remove them.
Feel free to PM me if you have any questions.