When he's gone for the day, take the housing off the machine and clean out the excess oil. Do not take the fly wheel off the machine. It has a clutch and very tricky to put back in the right configuration. No grease should ever be used on the gears and axles, just clear machine oil if they aren't self lubricating. No oil at all if plastic. If he used the spray type lubricant you need to get rid of all residue. It will collect dust and cause all kind of problems. Floss your tension disc with thread until the thread comes out clean.
I would have no problem telling my DH my machine he cleaned wasn't working like it should. He could sew on it and see what the problems I have are.