So I just changed the oil in the gearbox for my mowing deck. I unbolted the gearbox and drained the oil that way. It was easier removing the gearbox from the deck than I thought it would be. Anyhow, after seeing all of the shavings from the tractors hydraulics I was curious about the mower gearbox. I drained the oil through a paper towel and didn't find any shavings or foreign matter . I did notice that the oil was very dark. I've had it for two years and this is the first oil change to the gearbox. I'm wondering if I might have some kind of contamination (water) in my oil, or if this is just the color of oil JD uses?
Also, a question about the valve on top of the gearbox. What are we venting? If the gearbox gets warm/hot is the small amount of air it there going to make a difference? I haven't looked up the thermal expansion of the oil...so yeah what's the deal with that?