It's been a long winter. All in all a recipe for brake issues.
The caliper probably needs a full dismantle. Not particularly difficult if you take your time and are methodical. You'll need a brake wind back tool, caliper rebuild kit (includes 'o' ring seal for piston, and new dust sleeve), It comes with a solution to soak the rubber components in first prior to fitting. I'm assuming you have usual spanners, etc.
Jack up the wheel and support vehicle on axle stand, then remove brake pads and disc. Unwind piston. It could be seized, so placing a block of wood behind the floating caliper and using applied force while unwinding usually does the trick. I use a brake pipe clamp, but others aren't keen on them, so make you're own call. You can also put cling film over the brake fluid reservoir to minimise fluid loss. With the brake piston out, remove the 'o' ring brake seal. Clean the piston bore, and refit new 'o' ring and lube with a little brake fluid.
Remove existing dust boot, etc. Check condition of piston for any corrosion. Light surface marks can be removed with very fine wire wool and a little mineral oil. Dry off. Now fit the new rubber dust sleeve that's been soaking. Clean off fluid, and dry. Use a little Lockheed red grease under dust sleeve when fitting.
Open brake bleed nipple, remove clamp and open brake fluid reservoir cap. Engage rubber dust boot in the aperture recess on the caliper. Wind the piston back into the caliper until its fully seated. Close off brake nipple, etc.
Good opportunity to clean brake disc with methylated spirit, wire brush caliper and check general condition of pads. Use a little copper grease on the backs of the pads, etc. Check condition of rubber brake hose. Any cracking or bulges - then replace. The 10mm bolts on the floating caliper need thread lock. The brake sliders should be lubed too.
Now the handbrake. Chances are its seized. Release the bolt on the back of the caliper. From memory it's 13mm. Prize off return spring (taking note how it fits). There's a smaller bolt that holds a fitting plate. Again from memory it's a small allen key or star drive bolt. Make sure its clean and the tool is seated properly. Strip this bolt and progress will come to an abrupt halt!
With the backing plate off, clean the thread on the back off the caliper, grease with a decent waterproof marine grease and fit backing plate, return spring, etc. Before fitting handbrake cable again, lever it forwards and backwards and work the grease into the mechanism.
Check the condition of the handbrake cable. Any fraying, then you need to replace. There is adjustment (expanding yoke, locknut, etc) on the cable, but you'll need to spray with duck oil or WD40 a few days before adjustment.
Brakes will need bled properly afterwards. Use DOT 4 fluid, etc.
Audi do exchange service on new calipers if the above sounds like a long haul. Good luck.
