hello, new here. My 79 R600 recently developed an oil problem. a few weeks ago, it blew out a rear wheel seal. I pulled it into the shop and found the top gear case (the carrier housing) to be very low on oil. I filled it back up and continued hauling for a few more hours to finish up a project. the next day I checked the diff fluids again, as it leaked a lot out of the bad wheel seal and found the carrier housing was low on oil again (after only a few hours of driving and sitting overnight). the lower case, was over full by quite a bit. I was in the middle of an important job and needed the truck for a few more days, before I could tear it apart, so I ran it a few more days, and each day, the top case was low a quart or two, and the bottom was over filled. It has no other leaks besides the wheal seal. I assumed there was a bad seal in the carrier housing, so I removed it and can't find anything wrong. infect it appears that right about at the level of the fill plug, there's a hole that connects to the other side (passenger side of truck) that is open to the bottom housing. so, I'm not really sure how it wouldn't leak down. The only other thing I found, was that all the bolts that mount the top housing were nice and tight except for the 3 hard to get ones were snug, but not very tight at all. including one of the ones inside the cover. if that bolt were crazy loose, id assume that was my problem, but I just can't imagine losing a quart or 2 of 90w day through a snugged-up bolt. I don't see any obvious cracks, and the vent wasn't plugged. I'm kind of stumped. I hate to put it back together without fixing anything. Its leaking bad enough, I expected to find an obvious problem, but I didn't. Anyone have any ideas? is this common? I've been running Macks for almost 20 years, and this is my first time ever having to tear into a rear end. although I have noticed it does seem like they normally VERY SLOWLY loose oil from the top into the bottom.