There used to be some great chain cleaning / lubing concoctions, which came in a bog tin which you heated up on the hob with the chain in them. The idea was to get the warm and runny oil into the nooks and crannies of the chain.

Don't know if they're still available?

If not, you could try removing it and giving it a good soak in chainsaw chain oil (not engine oil) as that is cheaper than bike chain oil as it doesn't have any any fling properties.