Therefore, I have a straight-through exhaust now that is in pretty good condition and isn't needed. Has the name Walker on the box. I know nothing about exhausts - even less about ones fitted to early 912s so if anyone can advise if it's going to be of interest to any fellow DDKers then I'll pop it in the Parts For Sale section. Haven't even had time to clean it up, hence the grease etc, but it would be a shame to just dump it!
