chains. I was glad o see the back of them but then Mrs G got herself a Hornet.
A scottish winter on salty roads is hell on a chain, but that just looks like surface rust. the way to check is with the chain wear sticker beside the rear axle. this will show you if the chain has reached its service limit.
I'd advise fitting a scottoiler. The chain life is so much better, and the chain maintenance is so much easier. The scottoiler website has loads of instructions for fitting the device. I've done three so far - it's not that hard.
I've been told not to use wd40 on chains and bearings as it can force the oil out of the o-rings. I would remove the back wheel, let the chain pass through an oil bath (a bottle of chain oil will work) soak it, clean it up and remove the excess oil.
And always replace the chain and sprockets as a set.