Sorry Jureb, been a manic monday here, gas board replacing pipework in road and need access to property.
Anyway, the scrap one is so floppy and loose where I destroyed the barrel , but I took the cover off spare on the unused 78 and there is one still on there, (out of sight, out of mind).
The outer does not turn independently as said, it's part of the lock. With the key slot vertical, insert key and turn 180 to the left, so the key is now upside down to the position you put it in, the barrel with key now pulls off. I have tried several times and works, twice I needed to jiggle the barrel and key, the key wasn't all the way in.
Lubing yours cannot hurt, but be very wary of heat, sorry if I am teaching you to suck eggs, but the cover is plastic, and you could get heat transference to that, the wheel and possibly rear door.
The one on my 120 wouldn't even let the key in, yet alone turn, so as yours is turning, there is hope, its not like a normal lock as such.
Come back if no joy, I'll try to be quicker then. Cheers.