That makes more sense. For that, I would recommend going back to the factory recommendation, see what it looks like after a thousand miles or so, and go from there.

 

Yep my manual said GL5 80/90w so gonna drive it for a bit drain it, inspect it, and go from there.

Guy I bought it from didn't really drive it all that much as it was his 3rd vehicle. He drove it enough to melt the transmission/transfer case vent lines, and then he parked it for 6 months before selling it. It was leaving a good drip of TC fluid in just the first few days I had it parked so I don't doubt it probably leaked out probably 1/2qt if not more on the 2.0HR ride home. The pinion seal on the rear diff looked at first like it was leaking, but after wiping stuff down it was flying off the TC and landing on the shocks, and rear diff.

Fun discovery on the test drive was the metal to metal sound it had.... Found the RR hub was leaking 80/90w onto the rotor/pads and it quickly went metal to metal. When I replaced the brakes, and the RR hub, I pulled the ABS sensor and it was like removing a drain plug on an oil pan and at least a cup of 80/90 poured out of the internal part of the hub. I've seen rear O-Ring's fail and leak, but I have never seen a P38/D2 hub fill up like that before.

I have it leak free now except for valve cover gaskets, but that is going to have to wait until I get new plug wires/insulator boots, so I can pull the intake and do it all at once along with new coils.

This 04 D2 has been a lot more work getting back up to spec vs my 98 D1, but I bought it because I wanted something to tweak. Once the TC checks out I'll slap some RP gear oil in the TC. I'm not a big fan of RP engine oil, but I do like their gear oil.

 

Just remember, when your truck was produced, 85/140 gear oil was not on the market. I always recommend paying a little more for the heavier grade oil, lot cheaper then repairs down the road.

 

Update - I cleaned everything off real well and could tell the leak is coming from the transmission to x-case junction.

Drained the oil, added half a bottle of the standard Blue Devil Stop Leak (not the transmission one) and Lucas 85/145 gear oil. It's been 700 miles and so far no drips; I'll continue to monitor but so far I am impressed based on the size and speed of the leak I had before.

Before, the average spot in the parking garage at work, after a 40 mile drive, was about the size of an iPhone 4.

 

If it gets to be the size of an iPhone 6 or any Samsung, you probably want to think again.