Posted this on VMF:
Not sure if anyone is aware of the H-26 Service Campaign that had to do with Disc brake master cylinders. I have a copy of the letter date 1/29/65 sent to dealers describing what to look for and the procedure for replacement.
Specifically, any disc brake master cylinder with "618467" and a "4" on the bottom were supposed to be discarded. This is all fine and dandy.... EXCEPT! Has anyone ever noticed the endless supply of NOS disc brake master cylinders sold on ebay over the years? Well guess what... I have purchased 2 of these... and you guessed it... they both have the number above cast on the bottom! Evidently this stash of "NOS" master cylinders could quite possibly only consist of defective units.
Just a heads up and FYI!!