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I know this thread is older but here goes. I have a 2021 3121RL with the same issue with the same 9200 awning motor. I was able to get a replacement from Keystone through my extended warranty plan after little help from Dometic. I decided to do a repair on the one that failed so I have a backup. It did appear to me that the gear was molded to the shaft around a serrated area and a hole in the shaft which the glass filled nylon flowed. This is the point of failure, motor drives the gear but it just slips on the shaft after it fails. My guess is part of the failure comes from retracting the awning and once it touches the side of the camper, if you continue to hold the retract button it puts additional strain and torque on the joint, weakens it and eventually fails. There is no torque limiter or slip clutch to protect it. In my case it didn’t even blow the fuse.
After seeing where some others had attempted to repair over on another Forum, I decided to make a new flanged shaft and modify the gear to marry the two together. I bored out one side of the gear just deep enough to remove the ribs and hub. Also bored the center hole to 10mm. Added holes for the rivets. The new shaft is a replica of the old with a flange integrated into the shaft-all one piece. It also has holes to accept the rivets. The head of the rivet only protrudes slightly but there is a flange bronze bushing in the gear housing the shaft goes into that provides the clearance needed. It went together quite nicely however I have only bench tested this since I put a new motor on the camper and will use this as a backup. I had a local machine shop make up the shaft and modify the gear for me. Fortunately I know the owner so he gave me a break on the cost. I feel that this design is stronger than the original, time will tell…If this is something you are interested in doing, and have access to a machinist, I have pdf drawings of the parts made and more photos.
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