I emailed Rockwell recently about their 6C workmanship even before seeing this post ... they said they have put a fix in for the threading for the 6C .."However, the thread on the new 6C is improved to make it more durable". Even if you buy a new razor- I would try to get a new cap for your 6C from Rockwell since they know they have a known defect. Did they get back to you?
Sounds like you are set with the Karve... good luck!
Sounds like you are set with the Karve... good luck!