Brake pistons sticking

[Mctomo]

My brake has started locking onto the disc, like the pistons wont go back into the calliper.

I have tried taking them out, pumping the piston all the way out and covering it with GT 85 and oil, but after about an hour it sticks again, making the bike un-rideable and a farse to keep fixing?

Any ideas of how to fix it better? The brakes all bled up and stuff, just keep jamming on!

Thanks!

[AdOsborne]

Brake cleaner would be better get all the brake dust out of it give it a good clean and try it! It is happening on my mtb atm!