As I was researching wheel motor upgrades for the 425 twice, I found that some series of motors have case drains standard, some are optional (simply requiring drilling/tapping the motor's body either at the factory or later), or have no provisions at all. Light duty motors commonly do not have them. Severe/heavy duty normally come standard, while medium duty may or may not. The 28.3ci White RE motors that Surplus Center was selling for about 25% of retail, apparently has no provisions for case drains.
IMO, Tazewell likely does not use case drains on the 4xx series simply due to cost savings on the plumbing required and the cost of the wheel motors themselves. The 4xx series is not intended for as heavy/demanding use as the larger tractors, and they're trying to keep them at an attractive price point. The diesels, with an expected/designed service life of 3000 hours plus, and heavier use, demand them, in comparison to a 4xx homeowner/prosumer machine with an engine designed for a 2,000 hour service life in less demanding use.
But, I used/abused my 425 far above its designed capabilities...
