@afish70,
I got the same error code on my EC5 on October 3rd, but I only just noticed it last night. The only motor I can find in the schematic (in the owner's manual) is part 51921, "RPS MOTOR GEAR DRIVE ASSEMBLY". So if the error code is right, then replacing that motor should do the trick. My local technician charges $98 for the first 15 minutes, and then charges by the minute after that. I was thinking I could get a new part under the warranty, and then just replace it myself. However, I'm having trouble finding the part online. I've reached out to Rainsoft customer service to ship me the part. We'll see if they do. The "lifetime" warranty is pretty useless if you have to pay hundreds of dollars all the time just keep this thing running.