Just replace the motor with another brushed . If you Never clean them out and lube the Bushings, they will always fail much sooner than later. Motor cleaning, and lubing should be done often, like every 5 runs or so. As the brushes wear, the dust from the brushes fouls out the whole motor, and causes it to get much hotter. Shorter run times results as well. Need to clean out the dust and dirt often and lube the Bushing at both ends.
Buy yourself some Automotive Electrical Contact spray ( safe for motors and evaporates fast) and some Synthetic Oil. Spray out the motor once removed, Flush it out until no dirt comes out anymore. Brushed motors need regular maintenance. Also, the brushes just normally wear out. But the stocker motors are cheap to replace when they do. So its best to maintain them more, or just expect replacing them frequently . Brushed RC motors are this way. Nothing new. Get used to this. You can also buy A Rebuildable brushed motor and replace the Brushes as well. They have more performance to them as well as Ball Bearings instead of the Cheap Bushings. Still clean them out etc. But the brushes are replaceable. How I fly with all of my Brushed Crawler Rebuildable motors.
I wouldn't bother to upgrade any Mega platform to BLX.
Better to just buy a new 3s BLX 4x4. Cheaper this way.
The only Upgrade I would advise is a Brushed Rebuildable motor, and Not go with a BLX (Brushless setup). Get a 10T or 12T Brushed rebuildable motor. Have some new spare brush pairs on hand also. There are videos in regards to servicing rebuildabale motors. And Rebuildables aren't that much more expensive over a sealed stocker motor.
Look to Holmes Hobbies Brushed motors if you want the $best$.
Otherwise, AMZ has Apex and other less expensive Rebuildable brushed motors.
>>>It is always advisabe to Break-In any new Motor or when you change out to new brushes.
The brushes will last longer and have better performance. Because the Brushes will seat better to the Commutator,
Search for videos on Brushed motor Break-in procedures and maintenance. The Arrma manual will never show this.