My 2014 Ram Eco Diesel's oil cooler failed and injected 1 to 2 quarts of oil into my cooling system. The dealer flushed the cooling system several times and replaced all hoses, oil cooler, radiator and thermostat. I still get small amounts of oil in the coolant reservoir. Will the oil degrade the coolant? Can it be bad for the engine?
Is the oil still leaking into the coolant reservoir ? If so then yes it will eventually affect the cooling of the internals of your car once enough oil gathers in the reservoir.
If not and it's only a small amount(say a thimble full) then it won't do any damage in the long run to leave it in there although the dealer would probably recommend you flush it a few more times to get rid of the small amounts of oil.