Brake Caliper Leaking: More than Seals Required ?

[RockyTop]

My mechanic mentioned that one of my Alcon/Baer 4 piston front calipers was leaking fluid. I am about to go up to VIR for Viper Days and need to correct it. I just ordered all new seals for the calipers. One sugested cause of the leakage was a "mushroomed" piston. Until we get it off the car, we won't really know. As I am ignorant on this and many other subjects, can someone tell me if mushrooming pistons is common ? My calipers have about 3 years of street abd track driving.

Are there other components of my front calipers that I shoud anticipate needing repair/rehabilitation ?

 

[HP]

I've never encountered a mushroomed piston, even though I've
seen plenty of pistons with scuffed up heads(still functional)
The normal things associated with leaking calibers is faulty
seals, caused by things like torn dust covers or contaminated
brake fluid.

 

[Tom F&L GoR]

Assuming that the open end of a brake caliper piston is facing the pad and away from the fluid, how does it mushroom? Anyway, if it does, would it not get stuck in the bore?