Hi @pagedog ,
Can’t find a service manual for the printer but either the laser scanner assembly service station unit may be faulty (same scanner unit is used in printer for both ADF and platen glass scans or copies) or the control board for the scanner unit may be faulty.
The spare part number for the laser scanner assembly service station is B4U34-60014.
If you search online using the part number only you might get suppliers - most say out of stock, call. It isn’t cheap so it would be an expensive gamble to replace it and see if that resolved the problem.
Here’s a link to all the parts for the printer.
You could always contact the supplier in the link and ask their opinion as to what is the most likely cause of the problem. It never hurts to ask ;-)