From TDIClub

Brake fluid

The brake fluid specification is DOT 4. DOT 5.1 may be used, as it is compatible with DOT 4 but has higher boiling points. Do not use DOT 5 silicone brake fluid. Do not use DOT 3 brake fluid that is not also labeled as DOT 4, since it has lower boiling points.

Commonly available DOT 4 brake fluids include Valvoline Synpower and Castrol LMA, both about $5 per quart.

Brake fluid should be changed every two years, regardless of mileage, according to the owner's manual.

Brake lamp switch

The brake lamp switch may fail, causing the brake lamps to be inoperative, or always on. On cars with an automatic transmission, the failure of the brake lamp switch may prevent shifting out of park. The glow plug warning light in the dash may flash. A VW-specific scan tool like VAG-COM will be able to determine that the brake lamp switch is causing that warning.

In the US, a4 platform Jettas (but not Golfs or New Beetles) were recalled twice for the replacement of the brake lamp switch.

The brake lamp switch itself costs $5 to $15 or so; there have been several revisions (the ones with purple or green parts are newer than the all black ones). Installation is described here: http://ns.istop.com/~benadine/brake_switch.htm

Rear brake pad wear and brake dust

On some years, the original rear brake pads wear quickly and generate a lot of dust. It is common to see some year cars (e.g. 2001) with lots of dust on the rear wheels, but very little dust on the front wheels, since the front brake pads were less dusty. Newer VW OEM rear brake pads (made by TRW instead of ATE) may be less dusty than the previous ones.