Rear brake - no pressure

The rear brake pedal on my R1 was able to be pressed all the way down with no effect on the brake, so I assumed it was the master cylinder so I replaced it yesterday with a second hand one from the wreckers (they assured me it worked
) but I still have no brakes.
I've partially bled the system (got interupted yesterday and I'm at work today
), fluid is coming out of the bleed valve so I assume the master cylinder is working and the brake lines aren't blocked, but the pads/pistons are not moving. The R1 has two bleed valves on the rear brake calliper (one on each side), do I bleed both just to be thorough?
Could the pistons be stuck, is it worth taking the calliper apart to check? I don't have any replacement seals etc at home, is this a problem?
I'm supposed to be going to a track day at QR tomorrow and if I have no rear brake I assume it won't pass scrutineering, I just want enough brake to pass scrutineering. Luckily I have two bikes, I may have to take the ZXR instead but was looking forward to testing the R1 out. Anybody got a rear brake calliper for a 2000 R1 laying around

I've partially bled the system (got interupted yesterday and I'm at work today

Could the pistons be stuck, is it worth taking the calliper apart to check? I don't have any replacement seals etc at home, is this a problem?
I'm supposed to be going to a track day at QR tomorrow and if I have no rear brake I assume it won't pass scrutineering, I just want enough brake to pass scrutineering. Luckily I have two bikes, I may have to take the ZXR instead but was looking forward to testing the R1 out. Anybody got a rear brake calliper for a 2000 R1 laying around
