Last year I was searching for worm drive circular saws.

One had a sealed gearbox, the other cost 10$ more and required gear oil changes.

Guess which I bought.

Auto Engineers get trumped by the bean counters every time.

 

Just my .02 cents, I don't generally bother changing the rear axle oil on most vehicles. From my observation is that if you treat the rear axle decently, not tow with the vehicle or heavily overload it that the gear oil will stay in good shape. I have drained a few that had seal leaks and well over 100k miles and the oil looked like it had been just added from a bottle. That said I have seen one where the oil looked really bad but I knew the owner was not the friendliest with his vehicles. He drove the vehicle for quite a while with a worn wheel bearing and the seal leaking onto the brake shoes which is a great way to set your brakes on fire.

On engine oil changes I run my oil between 5 to 7K miles I change the filter between 1.5 and 2K miles and I have a late 70's engine in my car with 97K original miles and my van though a 97 has over 370K miles so I am not surprised that it works for me. I recommend to every one to try this for I have observed that the oil will clean up quite a bit in color by doing this which tells me that even though the filter had not clogged up (I have cut a couple open to verify what was in them and did not find much of anything) that the fresh filter does a better job of cleaning the current oil. I have not tried this theory on any newer low mileage vehicles but would be interested if anyone does try this and what the results are.