[size=24]AÏDA - YOU DID IT!!![/size]

Thank you, and those that gave the answer!

Tell Jon that I got a brand new set of single-sided tumblers with my cases. (phew!)
I made a couple of minor changes to lines 3 & 4 of your instructions!
BTW - the tab is not visible at all, with the tumbler in place.
I ended up using my [almost] 90 degree right-angle-tipped screwdriver to press on the illusive tab.

Happy Motoring!