MGTF Petrol Filler Cap

As Ive been roped in to help a friend get his car back on the road, I'm struggling to figure how to reassemble the filler cap. This has been in parts for about 6 months, and he has forgotten how it goes together. What I thought would be straightforward is somewhat stumping me. I can't seem to find where this thin ring goes (pic 3/4) I thought maybe it sits inside, and the centre key piece snaps down inside. Even out of the unit, the thin ring will not slide over the body of the centrepiece, and it all seems too tight. All the articles I've found so far seem not to mention this part at all.

Right, finally the solution. When the lock unit is out of the centre portion, the centre unit splits into blue cover and top and bottom black unit. The thin ring fits between the two halves of the black centrepiece. In turn, this all easily snaps back into the polished ring. I did remember when doing my engineering apprenticeship, the solution is always to crank up the swearing, which always helps.

glad you worked it out, incidentally why was it dissembled in the first place?
Mike

My friend took it apart to polish the aluminium ring, but got side tracked into a multitude of things car and family orientated. All being well, I hope to get his car ready for MOT by the end of the week, sadly the summer's on the Wain but at least It's ready to go again.