Collision sensor not working, Roomba stops with uh-oh only

My Red, early model Roomba 4100 stops and gives the uhh-oh error with no follow up beeps when it bumps into objects mostly from the front or right side of the bumper cowling. After pushing the clean button again it seems to drive forward lunging a few times and then changing direction until it has another center to right side collision. I believe the collision sensors is malfunctioning. I opened and blew out the vacuum 2 days prior and seemed to fix this problem for only 2 uses. I tried opening and blowing compressed air on all the sensors, checked the mechanics, inspected all the wires and connections but can't make the problem go away. I have not been able to find the exact manual for this unit. As such I do not know what all the beeps and flashing lights mean when I run the diagnostics since it seems different from later medel Roombas.

Either how do I diagnose if this is a collision sensor on the nose, or inside where the right collision bar connects by the mother board, or if it's some circuitry problem, or other problem?

Or does iRobot repair these? Or are there services that you can send them away for repair? Or should I just buy the $170 other brand, hepa filter, highly rated robot on Amazon?