If the RMS is leaking, it should be replaced just as any other seal would need to be replaced if it had perished. If the only issue is the RMS, the shop telling you that the entire engine requires replacement is consumer fraud.
Most folk would agree, that as long as you lose less than a quart of oil between oil changes then everything is acceptable. Not great or even good, but acceptable.
Personally, I dislike any sort of oil leak as a matter of principle. But then I also dislike dirty engine bays...
Seek a second opinion and if, as I suspect, you are told that the RMS needs replacing and that is all it needs then report the first shop to the BBB. What they are doing is illegal in most states.