This is something I have looked into thoroughly. As far as I know, what Stick has suggested is the only way of re-keying a gas cap with two-sided key (for late 280SL). This idea was first implemented by Mark (Iconic) and I followed. The end result is satisfactory: a single key now works for ignition, doors, glove box, trunk and gas cap, as intended by MB. (According to my mechanic (Jim Cosgrove of Oldtimer Restorations), who actually did the barrel transplant, there is quite a lot of work involved though. He didn’t charge me for the time spent, but he would not agree to do it again for another customer!)
Lakis Akylas
71 280 SL, zf 5 speed, ltd slip, anthracite grey metallic (172), light grey MB tex (136)