With mating/sliding parts lightly lubricated with fresh brake fluid, insert the fluid seal in the caliper, slide the dust seal over the piston, offer the piston/seal to the caliper and work the piston around like stirring a bowl to help the dust seal pop into place. Once seal and piston are fitted and ready to be rewound fully into the caliper, either use a proper tool or improvise with wide pipe grips to grip the very end of the piston and rotate bit by bit to screw it in.

Torque on disk callipers? - Skoda Octavia Mk III (2013 - 2020 Torque on disk callipers? - Skoda Octavia Mk III (2013 - 2020

Although the mechanic said it was letting dirt in I can't see any full splits in it, however that is only visual inspection and I am aware that it could be split and I'm not just seeing it. If there is damage when I take them apart I'll replace them. I think I am getting myself mixed up, you are correct there is no need to remove it, I was remembering when I had to change something else which required it's full removal!

There is nothing wrong with people maintaining their cars, but these cars have modern materials, processes and sometimes need particular tools. Thank you, I thought it was a M14! I'll buy one tonight, they will have to come off to get at the seals properly! Having read what the others have said it would seem these ones wind out!

spline bolt as it - BRISKODA How can I remove the caliper spline bolt as it - BRISKODA

Thank you to everyone else also, this has given me far more confidence to do the work and what tools are needed! With piston still protruding fit the dust seal, a little red grease helps push it in the recess. Once in secure with the metal ring, easiest to keep the open end of the ring away from the bridge of the caliper. This often the hardest part as you need to push the ring into the recess, which is allows a fight as you try not to puncture the dust seal. Once seated pull the dust cover out so the outer end fits into the recess on the piston. Move the piston in and out to ensure the dust cover stays in place.Depending on the depth/amount of any corrosion you may be able to clean it up with some very fine sandpaper. Obviously this will only be a temporary repair but it will last a while - monitor for fluid loss. There will be all the usual people that say they have re-used them with no issue etc etc but that is what it says quite clearly in the factory manual. Personally I will occasionally use some of the less critical bolts again, only if I know for certain they were stretched no more than once previously. Bigger ones or anything on my brakes I replace each time. Wind the piston in, remove the arm for the handbrake from the rear of the caliper. With a rubber hammer or a piece of wood tap the bolt the handbrake mechanism into the caliper. This will push the piston out a bit, then using air blow the piston out. A foot pump will do if you don’t have a compressor. Use the plastic tapered connector that comes with pumps and apply it to the brake pipe inlet after you’ve removed all the brake fluid. Otherwise use some grips to remove the piston. I wouldn’t recommend reusing the pistons as replacements are cheap enough. The piston will come out with the handbrake mechanism attached and it simply screwed off from there. Edit. This is all from memory but it should cover it all. Don’t forget to clean up the pad carrier and lightly grease the slider pins.

4147 Ball Joint Spline Bit M14 - for VAG - Laser Tools 4147 Ball Joint Spline Bit M14 - for VAG - Laser Tools

They are tightened by first a torque then a further angle to stretch them. (Like 70nm + 90degrees) it is what stops them undoing and they are single use. It says under each of these torque settings in the manual “replace after each removal” The reason they are tight is they are stretch bolts. VW group use them on most of their suspension and brake components.