The recommended lube is a bit difficult to find- its a 600W heavy oil, not so much a grease. I believe a lot of people are using John Dear corn head oil (a combine lube) with success. I think GM discontinued the factory recommended oil several years ago. You used to be able to buy it at Chevy and GMC dealerships.
Some people have been able to make what the jeep folks call "knuckle pudding". Its a 50/50 mixture of grease and 90W oil that resembles the consistency of the 600W oil. 140W gear oil is just going to leak right out of your steering box and straight grease is too thick.
