Norman, Hopefully you located the leak. I can tell you this much. If you replaced both Norgen valves at the rear and the LR is still leaning then There are only two possibilities remaining. 1:The airline from the valve has a leak maybe from rubbing on the chassis or at the fitting on the air bag. 2: the air bag has a leak. The airbag would be my target. If you have jack stands you can inflate the rear bags as far as they will go exposing the entire bag, get under the coach and blast the entire bag with soapy water. I have also seen the threaded fitting coming out of the top of the airbag where the airline connects, get cracked. Check the tag axle bag also.
Let us know how you make out.