I'll explain, and yes I'm ready to be scolded.
I'm in southern Alberta. I've seen it drop down to -40c but of course I don't use the tractor when it's that cold. To much of a wimp. I have run it at -30c but that's when it was in a heated shop and plugged in. I've never had hydraulic problems before even with it sitting outside in -20ish weather. If it started, it was good to go. Now when it gets down to -10c, I have to drive it up the road a half mile and back to warm up the oil, then it's fine. Now the bad part.
Keep in mind times have been hard. You know how sometimes you can afford to spend the nickels but not the dimes. Doesn't make sense but that's how you're forced to operate. So I find a store that sells bulk oil in their automotive department. I asked a local mechanic about it and he says he uses it in some of his older cars that burn oil. He also used it in an older tractor and started having trouble with the hydraulics, but thought it was coincidence. I hadn't talked to him since then.
So now I'm having trouble. I'd thought about the moisture thing, and the oil in the trans does look kinda iffy. Not as bad as what's in some pictures on this forum but not quit right either. So only having nickels to spend, I bought the same oil that we've been using in years prior. Since the tractors sitting under a shelter right now with no heat I have to wait a couple days for a break in the weather to work on it. I'll drain the oil, pull the filter and clean it up.
One question though. Is pulling the plugs and waiting enough? Obviously there's going to be some oil left in the system. The pump, the tube from the pump to the transmission, that kind of thing. Once the filters out should a guy crank the engine a but to force these areas out?