WOW. Thank you for the link. I'm used to taking PCs apart from behind etc. but never by removing the screen. In retrospect it is possibly obvious as there are no visible torq screw heads any where else.
Mac lovers best quit here... I'm basically an engineer/improviser.
At the moment, thinking whether to go out and look for a 'proper' suction cup or improvise. Well, the engineer part took over and I used what was available. Worked fine (I did give it a good clean first) and voila the innards are exposed. Now it is simple.
Thanks Ash you have saved me an expensive visit to the Apple store.
BTW the iMac was under extended warranty, unfortunately expired. I had booked an appointment at the Genius bar but this has now saved me the expense.
I used to build my own *****ws PCs but converted to iMacs years ago. Until now much more reliable/stable. Now I'm even more confident having actually got inside one