Many thanks John,
I have just written the following and now realize you tentatively identify the mystery plant as Andromischus cooperi , both close enough I think
" Yesterday I posted photos of an UNKNOWN SUCULENT. I had tried many times to find out the name of this succulent, looked through my succulent and cactus books, searched the internet even put a photo on Google images but no success
I checked all the series of stamps from South Africa which I have, still no success
Yesterday afternoon I thought to look up Graptopetalum paraguayense another plant which is easily grown from the leaf and came across the website SUCCULENTS and SUNSHINE. where the types of succulents are sorted into categories.
Ignoring Agave, Aloe, Crassula and others I clicked on Other Succulent Varieties and there it was, the mystery plant, Adromischus maculatus.
As usual the plant has several synonyms a couple are
Adromischus rhombifolius and Cotyledon maculata ."