Whilst putting a new set of pads in my hayes hfx brakes last night pre-ride, I was using the original plastic taper edged spacer to push the cylinders and pads back in far enough to allow me to slide the disc/wheel back in and to my horror I realised that some brake fliud had leaked from the caliper, I guess from the piston. After cleaning up the oil I put the pads back in and gingerly tried the brakes and they seem to be fine. What happend, do the pistons have seals, can they be replaced? Anyone?

Yes there is a rubber seal between the piston and the caliper body. They are replaceable if you can get spares – which I don't know about for those brakes. Relatively easy to replace. As to why it leaked – did you clean the pistons before pushing them back? If not you could have pushed some dirt into the seal – it only needs a speck.

If the lever feels firm and stays firm when you hold the brakes on then it should be OK. Clean the brake up and then check for leakage again after holding the brake on hard for a minute or two.

Ah, I just seen the piston/seal kit on you know who, SIX NINTY NINE for each piston, two per caliper, four per bike. At least in the old days they wore a mask.

Thanks TJ.

Probably dont need seals, I've brakes 8+ years old with the same seals just happy – as TJ says, probably just shoved some dirt through and it'll either repeat the leak each time it passes or it'll come off at the back of the piston and never bother you again.