I bought an A 65 Lightning new in 1972, after 25,000 miles the bottom end seized, BSA were (just about) still in business and the Service Dept at Small Heath was still open so I took the engine in and they rebuilt it (I have the receipt somewhere, it was about £30!). The sludge trap was solid and I'd done all the oil changes. After that I fitted a spin off cartridge filter in the return line mounted under the front of the swing arm. I also ran A10's and never had the same problems with the sludge trap.
