Hi, Trying to date a Belstaff vulcanised rubber jacket. 2 zippers have evidence of replacement. They used a lightening and No5 ykk for replacements. The original on the left (right in pic) pocket is a Great Britain Aero zipper. The seams are quite crude in there sealing. Belstaff customer 'experts' don't help for jackets before 1980. Any help is appreciated.