Mini r50 2004 rear dust boot

[jimmyspeed]

I've just changed the discs and pads on the back of my sisters mini and after being stumped by the need to wind in the pistons, I've found a torn dust cover

I'm going to get a new boot and swap it, but is it as simple as popping out the piston and pushing it over or do I need to take the hole piston out and do the seal at the same time?

Any help much appreciated