Anyone who has ever purchased an Isetta or BMW 600 has at one time or another faced the fact that years of sitting round take their toll on the brake cylinders. All of my cars at one time or another developed leaks at the wheel cylinders. In the late 60's and early 70's when I first started driving and working on these cars you could hone them and hopefully stop the leak. Eventually, this no longer worked as the rust pits got deeper and the cylinders had to be replaced. Back then replacing the wheel cylinders or even the master cylinder was not that big of a deal. Cylinders were still available and at a relatively low price. Today, original ATE wheel cylinders are almost impossible to find. There are some non-original cylinders out there for sale, but they are not exactly the same as the originals. Fortunately, there is an alternative, you can have the cylinders lined with brass and return them to good operating condition.
Below is a sample of what the cylinders look like after rebuilding.
UPDATE:
I have converted over to include powder coating of all wheel and master cylinders. All items being shipped now are powder coated. All wheel cylinders are being shipped with new bleeder screws and original style dust caps.
I have been asked on a few occasions to post my address on this web page. That information is available on my "contact" page. I would perfer to provide that you contact me via phone or email before shipping any parts to my address. Please use the email address button below or the one at the top of each page. Thanks!