from CAT

The threads on most of the components of your Tiger’s brake system are fragile at best. It is easy to cross-thread a line into a cylinder, for example, and, once the threads are damaged, the chances for a good, leak-free connection are very small unless you can repair the threads.

One thing I do before refitting any of the brake (or clutch) lines is carefully run a 3/8-24 bottoming tap into the cylinder and run a 3/8-24 die over the fittings on the line to clean out and renew the threads.