I think pretty much all auto diffs do, mine does (87 Ford F150). Should be able to see it on top of the diff case - mine's just ahead of the brake lines, heading down toward where the ABS sensor goes into the diff (unless I'm looking at an odd fastener head). I just checked my tractor, too ('79 Ford 1700) and there's no vent on the front that I could see or feel (it's really dark here, but a balmy 45 F with a gentle Westerly breeze to remind you to pull down the sweatshirt when you're bent over the front tire) - just one up high on back under the seat. There is a lovely axle pivot grease fitting, and of course all the knuckle parts and such, down about axle centerline level. There's what appears to be a crankcase vent tube further back towards the middle, and it looks like I've got a small oil leak, or maybe it's just old fuel or oil spillage.
Maybe some of you guys with daylight left could check your 3010's and 3130's and such. And maybe your trucks. It'd be nice to compare wives' reactions to us hopping up form the PC, stomping outside with a flashlight, then back in, then out, then back in again (forgot to check truck the first time). She held off pretty well the first trip, and was making a good effort the second time, there, for a while.