The last few sets of cans I cut up had a rusty coloured thick and very sticky substance in them, it was an utter bastard to clean off. Without seeing what you've got I can't say if its the same but nothing I used, water or spirit based would shift it.

That would be oxidised veg oil, probably sunflower as it dries like yacht varnish. The rust as an oxide of metal speeds up the process. They added white oxide of lead in the old days to make paint.

springs wouldn't be rusty though

Slightly OT; a kitchen fitter I know told me to use vegetable oil on my Ikea beech worktops instead of the stuff you buy (at great expense from Ikea)for worktops. He reckoned that it dries hard and protects the worktop as well as the proper stuff (which contains linseed oil, IIRC).

Maybe I should have listened to him.