The planetary type gearboxes are manufactured by Eskridge in Olathe, Kansas.
The upper gearbox has proved troublesome, getting water in the top, where there is no seal. The water sinks to the bottom of the box and wrecks the seal on the output shaft and damages the bearing above the seal. Oil and water then go from the upper box into the lower main box. The main box becomes overfilled with oil. The upper gearbox runs dry and the main ball bearing on the output shaft becomes noisy. The planetary gear assembly has small rollers inside the planet gears which may also require attention. The upper gearbox may be removed with the main body and pinion gear remaining in place. Upper single stage planetary gearbox manual
There is an oil drain plug on the lower main gearbox body which is 3/8“ square and is about 1/4” above the bottom of the case, so not all the oil will drain out. There is also a smaller drain plug on the bottom of the output shaft case near the bottom bearing which is 1/4“ Allen hex. This is only accessible once the gearbox is disengaged from the ring gear and lifted up above the mounting plane. Lower double planetary gearbox manual
The pinion gear on the main output shaft will require heat and a puller to remove. The lower shaft has to be pressed from its upper bearing, heat needs to be applied to the upper bearing. The lower bearing can be pulled with a large gear puller from the lower shaft. The seal is wrecked in the process and needs replacement, reassemble with oil on the shaft and grease between the lips of the oil seal.
The upper planetary gear assembly has probably run dry and had water on it. It will need dismantling, cleaning and the roller bearings replaced as a set if there are signs of wear. The planetary gear unit is dismantled by driving the roll pin visible from the outside of the carrier inwards into the planetary gear shaft with a 3/16 inch punch. The shaft will then press out of the carrier and the roll pin can then be driven from the shaft. The roll pin is driven flush with the carrier body upon reassembly.