I am posting this in case anyone else has to chase down a source of case sealer at short notice (not an easy task as I now know) I took Myrtle for her MOT this morning and she passed (which was nice). She is still in my bad books due to the return of a flywheel oil seal leak in spite of me replacing it last Sunday. Anyway, after wise words from some on here (thank you Zed) and also some internet research I now know the exact method to use when I repeat the task tomorrow. One thing had me stumped though and it was where to get Curil K2 or Permatex case sealer from at short notice (no time for ebay sadly). Anyway, chatting away to the lovely man who did the MOT he showed me what they use, which is basically close to identical to what I was after and available from your local Vauxhall dealer spares department!!! It leaves a microscopically thin layer like Curil K2, doesn't harden and any excess that gets into the oil simply dissolves away (again like Curil). As its a very techy product it is called "sealer" and the instructions in the packet say "refer to vehicle manual" which is not very helpful. Indeed you need to know the part number to be able to order it even. The part number is 90542114 if you need any. Well £9 later here is my tube!
Yer can't beat a good dollop of Dichtungsmasse, I always say. If it's Vauxhall (meaning Opel), it's likely made by Elring anyway
It's good stuff. When the oil eventually finds its way out I just wrap gaffer tape round the leak. Used 20m so far, not one drip on the drive way.