Thanks Retropin, I'll give it a shot.
I've never had this problem either, which is why I am asking. Cleaned up many a pin over the years, but I admit I am wary of using anything too abrasive on an old playfield like this one.
The Mould seems to be only on the surface, but I'm not 100% on that yet. I'll have a go at it today and let you know the outcome.
Thanks Nino also, but I think I may leave the eucalyptus oil idea alone for this one.
