I understand this thread is old, but I found it super helpful for me in replacing my master cylinder.
When trying to find one of the "better" vented caps, I realized the original master cylinder has a thread adapter that can be inserted into my new master cylinder to allow the stock method of venting (and preventing rain to enter).
When trying to find one of the "better" vented caps, I realized the original master cylinder has a thread adapter that can be inserted into my new master cylinder to allow the stock method of venting (and preventing rain to enter).