I'm having more fun with my two 2.5TDi Qs, and their constantly sticking brakes.
On the Avant, I replaced both rear calipers using Audi bits, and both front calipers using bits from Brake Parts Superstore. This was over 6 months or so (as each one stuck!), completing the job about a year and a half ago. On my saloon, I replaced the two front calipers early this year.
Both cars had more issues with the front calipers sticking, in about May, and the saloon again now. I felt a little aggrieved that hers were failing after a year, and mine barely made six months!
Investigation showed the pistons on all four calipers had varying amounts of corrosion under the chroming, causing it the piston to stick. I did speak to the vendor, but to be fair, I had had them on too long to be able to blame the piston manufacture definitively, but I suspect his supplier is not chroming the pistons properly.
I've cleaned them up as best I can, but really I just want to change the pistons for good ones before I warp yet another set of discs, or bugger the good bearings I fitted to hers!.
Having had issues with other 'good' non-Audi parts that turn out to be cheap Chinese chocolate, who makes good quality brake pistons?