John,
I'd start looking for a different shop, it does not sound like they were all that honest,
You should see a new rear cover gasket or silicon around the cover, Do you see any indiction of a wrench marks on the cover bolts? Are they covered in dirt?
The oil might have been sucked out (vacuum pump) but I doubt they did that, and why anyone would put dirty oil back in is beyond me, did they add the additive if your truck has a limited slip? if its not on your bill/reciept go get some its around 8-10$ a bottle (I used 1 bottle of Amsoil LSD additive in mine) or better still for your own piece of mind get some good Synthetic 75-90 and change it yourself.
also if your truck has a full floater (mines a 2500 and it has a full floater and a Limited slip) make sure you jack up one side nice and high so that the oil will drain into the wheel bearing(hub) then do it to the other side, If you fail to do this esp after replacing axel seals or pulling the axel's out. you run the risk of siezing bearings and ruining the spindel,, the oil will work its way out to the hubs edventually, but the bearings could fail before it gets there, or you could pack the bearings with grease when its apart, to ensure the bearings will not fail. I've seen wheel bearings fail/sieze 200kms after rear end work was done, and the wheel bearings were not lubed, both times the mech thought the oil would work its way in there. BTW they were both 3/4 ton Chev's
Nick

 

this is good info. I have to check this vent!
second thing; 80,000 miles and never changed axel oil, question is;
1. how much and what kind of oil to use?
2. all I have to do is pull the cover, and change a gasket, then fill. right?

 

It takes 4 liters/Quarts..
John
They could have changed axel seals and NOT changed the oil.

 

And so, IF it was a plugged vent then you just keep replacing wheel seals???

 

Thanks a bunch for all the advice Nick

This has definately been a learning experience. It was certainly my neglect that the vent plugged in the first place because of my failure to change out the oil when required. I work for an oil company and we push our trucks pretty hard going through mud and water etc. and I have on occasion had the differential oil changed out for obvious reasons but my personal truck just rarely ever leaves the pavement and I just can't for the life of me figure out how the oil could look as bad as it does. However I'll get rid of it just as soon as I can get at it.

Would have never thought of that trick of jacking up the axle tubes to get oil to the bearings

Thanks again
John