I make house calls for sewing machines, so if you live in my neck of the woods, let me know. Sure, I'll go to the UK, but you have to pay my travel expenses. (You might find a more cost effective solution.)
His advice to use WD40 tells me his experience is not the best, IMHO. All the cautions you have received about it are spot on.
Don't use 3-in-1 oil either. It took me forever to unseize a machine that had been oiled with it. The patient lived, though, although she was in a coma for a while.