Managed to unknowingly delete a whole post, whoops!
Trying again: Thank you all so much for your suggestions! I have cleaned as far as I can, and oiled everything (possibly have gone a little overboard here, as I now have oil puddling on the inside of the base, and spitting out of the oiling holes when I sew...) I have kept hand turning the wheel, but it is still sticking when the needle ascends. If I try to put peddle to the metal, the machine tries valiantly, but in about 20 seconds the motor seems to slow. As a novice with vintage machines, do you think it might be time to pay someone to have a look, or is there anything else I can try? (The previous owner has admitted that she never oiled it: she was given it about ten years ago, and only used it a couple of times - albeit it one of those times was soft furnishings for a bedroom. It has been stored for several years since then - we have no idea how it was looked after previous to my friend owing it, although it looks barely used on the outside).
Thank you all again for your helpful suggestions - I don't want to give up on this machine, it does seem to sew a lovely stitch (yes, I forgot the needle was nudging the foot - it is correctly placed according the manual, with the flat side away from the balance wheel, and taking the needle clamp apart, there does not seem to be anything that could go wrong there, it's fairly basic and heavy duty - but it didn't seem to cause any problems, I may have been very lucky!), and I really wanted to introduce my children to the joys of sewing, but I am stumped!