We inspect our drums, [commecial trucks] if scored bad, or wore out of specs, we replace now even though we have a lathe that can turn them. Seldom are they bad and usually will go through a couple sets of shoes. If urs just has oil on them brakleen does pretty good, But I would clean them off as soon as possible as it does seem to soak into the linings...warehiem is now Fleetpride, at least here anyway and thats where we get our air brake parts from. commercial trucks that is.
I am curious why it leaked on all 4 at the same time. It has been super hot lately, maybe a little overfull or vent stuck, or all 4 sets of wheel bearings loose!!! not likely..LOL