UPDATE - For years our camera would work intermittently. It would go out for a day, a week but always come back on and work fine...then it finally wouldn't. It had been doing this for 2 years or so. At this point August 2023 it had been about a month since it last worked so I finally decided I had to do something about it.
I removed the panel and it was much easier than I thought to remove and reinstall ( I didn't buy any tool to remove it...I just pulled down firmly on it and it came off). One clip stayed stuck to the inside of the tailgate put I easily took it out and put it back into the panel and it was fine. No clips broke. I looked at the wiring harness and thought there may have been an issue with it as one wire seemed exposed but I had a mechanic look at it and he said it appeared to be like that from the factory. After unplugging the camera and reinstalling it, it came on again. We wiggled the wires around and it still kept working....so I put it back in, reinstalled the panel and it worked for a few more days then it just died again for a solid week with no camera - just the message to contact a dealer.
I found that Dorman has a back up Camera for a 2013 MKX. Part number 592-017. It was under $150 US with shipping on ebay so I bought it off a car parts seller "partscontainer" with 4.3 million items sold. It was packaged well and arrived ahead of schedule. This camera came with the large o-ring on it unlike most I saw on-line. I took the back panel down again and installed the new camera and it works perfect...the lines are on the screen, the picture is clear and the field of vision is slightly larger than factory.
I will update again in 6 months or so and let you all know if the camera is still working fine.
Thank you to those who offered me help on this issue...I appreciate it.