When you buy a Brake Wheel Cylinder a for your Beetle (or other VW), it comes complete with a Bleeder Valve and a Rubber Cap for the Valve.
This pair, the Valve and the Cap, were noted as VW Part# 113-622-475 and sold as a pair in the now-distant past. I cannot find Bleeder Valves with Caps sold as a pair. They appear to be sold, nowadays, as individual units.
Bleeder Valves for 1957 Beetles are distinctive: VW Part# 113-611-475
Later Bleeder Valves are as follows:
1955 Bus (starting at chassis # 20-117903) – 1979 Bus and Beetle 1958-1979, front or rear have a VW Part# of—113-611-477 (sometimes 113-611-477A).
Recently, our friend, David Brown, purchased a very nice 1972 Regular Beetle. One of the few things which it needed to be roadworthy was to have the Brake System examined and repaired as necessary. When he attempted to bleed the Wheel Cylinders, he found each Bleeder Valve to be stuck. An attempt to loosen (or “to crack”, as seasoned VW Technicians often say) resulted in the snapping of each of the 4 Valves. This meant new Wheel Cylinders. I have not heard of successful removal of broken Valves
When David first examined each Wheel, he discovered that none of the Valves had its Protective Rubber Cap. Why did David make a mental note of those missing Caps? Because the open Valves beg to be filled with dirt and moisture from the roadways. Contributing, no doubt, to corrosion within the Valve itself.
Another factor, of course, is the fact that moisture can accumulate within the Brake System. The Braking System is not a closed System—-moisture can enter through the Brake Fluid Reservoir. Moisture, which readily combines with Standard Brake Fluids, contributes to the deterioration of metal parts. Thus, a Bleeder Valve can corrode where it screws into the Wheel Cylinder at the threaded tip.
A Bleeder Valve, missing its protective Cap, coupled with old, tainted Brake Fluid inside the Wheel Cylinder where the threaded tip of the Bleeder Valve resides, can result in a Valve which cannot be loosened or removed.
Purge the Braking System perhaps yearly or every two years. This will assure that moisture does not accumulated within the System.
I encourage every Volkswagen Owner to protect the Bleeder Valves on his vehicle.