Thanks everyone. In the end I went with what I had about the house so I got the bulk off with vegetable oil (was curious to see how it would work and it was very good) and tackled the few very stubborn marks with acetone (carefully!). Now it looks and feels so fantastic, an entirely different machine to the taped up thing I got down from the loft. I suppose my Dad was just very paranoid about badly scratching the thing having spent a lot of money on it, and I guess with Leica's being valuable things you want to be able to get a good price for them if you re-sell. Funnily now it's clean I feel exactly the same but have found a good soft case to protect it when not in use; I have the original ever-ready case but I don't think I'd feel very safe keeping it in there! Thanks again.