OK Chaps. Update. I have been wearing the watch and just being careful not to knock it on anything and all was well. The bezel was loose but did need some pressure to remove it so I thought what the hell, I'm going to wear it. Yes, you've guessed it, this morning I was cleaning one of my other favourite objects - my Mercedes 300CE :
and when I returned to my domicile I glanced at the time and lo the bezel was missing. Aargh. I searched but it was nowhere to be seen. So, to the watch drawer I went and decided to steal a bezel assembly off a later generation MBW 5513 that I had lying around and see if it fitted. Snap off and snap on it went so then I really got adventurous and found an old faded de-pearled insert from an early MBW 1665 which I glued into the 5513 bezel (coz I like the wabi-sabi look) and here is the result:
Derisory comments and laughter welcomed