The pictures above are different types of gear boxes manufactured by Titan. Both the wheel box and T-box failed for common reasons. They both use bevel gears (ratio more than 1:1) or miter gears (ratio 1:1), when these gears rotate with torque applied they tend to push apart putting pressure on the bearings that are holding them in place. The type of bearing used is a sealed two bolt flange type. These bearings are not designed to take very much thrust, thus causing failure. The gears must be 90 degrees of each other with a fixed backlash for longevity and efficiency. All of these boxes were fabricated from sheet steel welded up in jigs. The light steel allows the box to deflect, and the boxes being out of square causes the gears to wear prematurely.
The Gen. 3 T-box was better but has problems too. The steel used on the shafts was too soft, the vent lets water in, and the top bearing won’t take the combined thrust that both output gears produce.
SOLUTIONS
Gen 1 wheel box; Install two bearings on each shaft, a good cover, grease at least once a year. See page 8 for modifications.

Gen. 2 wheel box; Install hub adapter, keep backlash adjusted correctly, keep oil level up. See page 7 & 9 for  modifications.

Gen. 3 wheel box; Install hub adapter, keep backlash adjusted correctly, keep oil level up. See page 7 & 10 for modifications.

Gen. 1 & 2 T-box; Replace with Gen. 3 T-box with modifications. Gen. 1 needs the motor/base mount, the Gen. 2 bolts in place.

Gen. 3 T-box; Install T-box upgrade kit.