99 front diff prob?

My 99 Jimmy was 3 days away from the end of the warranty when I noticed the input seal on the front diff was leaking a little so in to the dealer it went. They fixed it no problem so I thought. On the way home about 10 miles later I noticed none of the lights on my auto 4WD selector were lit. So I hit 2HI and after a brief pause ( I was on a hiway doing 50) it lit. Then I start noticing a hum in the front end and think I better check the fluid. After pulling the underbody protection package off and finding half my grease fittings dry (just had truck serviced) I pull the plug on the diff and stick my pinky in the hole and nothing!! 3 weeks have passed from the time I have had the seal replaced there is not one drop of fluid anywhere. My dealer was just to lazy to take off a piece of fiberglass to get to a filler hole!!

Here is my problem now. After having to put a pint of 80w90 in my front diff I still hear a hum. This hum sounds worse when turning left and almost dissappears when turning right. This is just the slightest of turns. Could I be looking at major damage? While the fluid in the diff was low the auto 4WD would go compleatly out if I tried to shift it. That stopped as soon as the fluid was brought back to proper level.

Please help. I am already 38 days from when the repair was done and 31 days out of warranty. This dealer and truck has been nothing but problems

2 batteries 3 oil lines 2 door hinges 1 alt 1 muffler 1 water pump 1 intake mainfold gasket 1 heater core 6 engine flushes in 2 years 2 climate control units 1 idler arm ALL UNDER A 6 YEAR 100,000 NO DEDUCTABLE WARRANTY TALK ABOUT BEING PSYCHIC!!