Oli....Got your PM. Might as well reply here so others can see....
You need to strip the calipers down fully externally, if you remove the handbrake adjust mechanism then you're into a world of hurt leave it in.
Ok
once you've removed the handbrake cable attach arm and the stop arm below it, the caliper will look like this (Its a B7 RS4 Caliper but the same process)
Now you will see that within the black seal that we are worried about burning is some crappy grease, you need to cut the end of a cotton bud and clean it up in there, the grease when hot degrades the rubber worse than the oven! use a TINY bit of solvent or worse WD40 to get rid of all grease and dry it out fully with some tissue paper.
Just to confirm this seal is just a dirt plug, the actual hydraulic seal is an O ring that abuts the dirt seal, its there to carry grease for the handbrake post to prevent corrosion and to trap dirt, if the seal is broken or split then I would use some speedtape to seal or "repair" it, this rubber seal "Flairs" out against the underside of the cable arm, this seal by TRW/Lucas is the same as the ones going back to the Mk3 golf so its easily available you've just got to dissasemble the caliper fully and for that you need some special uber long circlip pliers.
Just for "orientation" heres a pic of a B5 RS4 Caliper in for a full rebuild, this caliper was a persistent "Sticky Piston" offender which was cooking off pads and warping discs, so its been fully dissasembled, it'll get rebuilt with a new handbrake mechanism which is the same as Mk4 golf, the Mk5 caliper is exactly the same when dissasembled you can see the brass bushing in the alluminium casting that the handbrake post goes through, the O ring seal abuts behind that within the caliper, the dust seal that were worrying about cooking in the oven just sits in the recess it doesnt enter the caliper
Ok back to the caliper,
Once its clear of grease simply wrap it in masking tape and them most importantly wrap it in speedtape (Alluminium tape) its available from most engineering supply shops, its widely used in aviation circles so you can nick a piece if you know anybody (Mr Stoke Balloon has been keeping a fleet of Her Majestys helicopters airborne with this stuff and some self tapping screws for years) repeat this process to build up some protection and that areas good for the over Gas Mark 5 for 30 minutes
Some pics (Apologies for all Trevors (The boxer dog in the Avatar) toys in the pictures)
Some suggestions for a succesful outcome:
1, Use a M12x1 Bleed nipple to "mask" the threads oln the hydraulic inlet and a M10x1 bleed nipple for the bleed nipple outlet
2. Keep everything "STUPIDLY" Clean, it seems stupid to clean a caliper thats about to get blasted but once the caliper is off the car, remove the levers on top put the M12 and M10 nipples in and then COVER the caliper in plain fairy liquid and just RUB it yes RUB it keep going and then rub some more this is a great method for removing brake dust from a caliper before you disassemble
3. Once the pistons are out, do the fairy liquid thing with the outer dust seal and immediately immerse the bore seal in a zip top bag with NEW brake fluid in it and leave it there until you need to rebuild it. You DO NOT rebuild rear calipers (or any caliper for that matter) with dry seals if using new you need to soak them in seal conditioner or brake fluid for 45 minutes as the seals need to cope with not just in and out but also rotation.
4. When it comes to reassembly generally its a reverse process, typical gotchas are problems with getting the dust boot back in its recess, using a dental pick clean the recess in the caliper where the "lip" of the dust seal goes and without the piston dry fit the dust boot in there, to get the caliper reassembled you need to make sure the inside of the caliper is scrupulously clean with brake cleaner and that all the brake cleaner is wiped away or evaporated before reinserting the bore seal...... use VW part number G 052 150 A2 caliper rebuild grease to put it all back together.....you'll have fun and games getting the piston wound back in and the dust seal in place..... simply pull the dust seal past over the recess on the piston so its almost hanging off the bottom of the piston as you are rebuilding it - use plenty of grease so that the dust seal rotates around the working face of the piston as you rewind the piston back into the caliper.
Get in touch by Pm or email if you've got any specific questions
M10 bleed nipples and M12 bleed nipples you can get from Brakes International 01706 666999
DONT use any other grease than the VW stuff (Bout 20 quid) its lithium based and will dissolve in brake fluid its doesnt contain water.
These are BRAKES.....PLEASE dont take any chances with reassembly,if you are not sure please get in touch its a case of taking your time, I'll help anybody just ask.
Finally lets see the pics heres mine complete with Nickel plated handbrake levers for some bling
