I just noticed for sale on e-bay (item no.251667221588)the front brake rod suitable for the BSA WM20.Looks from the pictures that it may be a newly manufactured part rather than NOS.I believe that with one of these fitted front brake performance can be improved due to a shorter cable being used and therefore less "stretch" between brake lever and brake arm.Personally I'm happy with my cable set up but thought I would post it as a forum member may be interested.Mick.
I have an original one and the one on ebay is clearly a reproduction, seems to be well made I must say. These are typical pre-war things that BSA continued using during the first part of the war on the DeLuxe model military BSA's.