It sounds like the crash that damaged the cylinder has been the start of your problems. As you've already said the cylinder relies on tight tolerences to work properly, I guess because it has been lapped smooth there is now room for the oil to leak through.
Really I Only have two suggestions - one buy a new chuckking cylinder.
or Two - if you could put up with having to top up the hydraulic oil every so often, then you could redirect the waste oil pipe into a container and empty it every so often. That way it will not contaminate your coolant.
Sorry I could not have been any more helpful.