Stiff brake caliper piston - advice

[Hereward]

I replaced the rear discs and pads on my 2003 Touareg.

All the pistons could be pushed back in with my thumbs apart from this one which required a good squeeze with water pump pliers. I have no idea if it's subsequently re-engaged with the new pad or if it's now stuck in the caliper.

I just wanted to know what the correct protocol is in this situation - caliper rebuild or don't worry about it? They are 4 piston jobbies so it's not as though there will be zero braking effort from the affected caliper.

Thank you.

[Drive it fix it repeat]

Common procedure is wind them out and in a few times, could try and get some grease on the piston maybe. Presumably you had removed the brake fluid reservoir cap to allow space for the fluid to move? Check the rubber piston gator is intact, if its split or incorrectly fitted you may have a piston covered in shlt that is causing issues.

[ChampionRabbit]

Probably corroded and will need a new piston or cowboy fixing with some very fine wet and dry.

[Hereward]

Thank you.

Yes, reservoir cap was off and all 7 other pistons moving freely under thumb pressure.

Rubber seals looked intact but these are the original 2003 calipers so maybe time for a rebuild. Can't complain.

I will have another look with the pads off in the coming days and drive sensibly in the meantime.