well I went to the store came back parked then when I left for work noticed a pretty big slick of fluid under the center to rear of my 94 4.3 w. Not sure if it was there when I came back from store. Anyway would a leaky differential leak out Break fluid type liquid? I live near a hair Salon and sometimes share the side street so it could of been someone else's problem......Also I can tell that low 4wd works but can't tell if my 4 hi is engaged so because I can definitely feel the 2 low is my 4 hi working also.......isn't the lube more of a thicker grease type and how can I find out if all for tires spin without driving up a rocky slope?
The differential is wet looking but has always been that way for the year and a half I have owned it. Any insight would be great

 

The differentials have gear oil in them. Not brake fluid. It will be a darker/thicker oil. You will need to check the level to be sure that your truck is safe to operate without causing damage.

As far as the engagement of the front axle goes, jack up the front of the truck while in 2HI and make sure that the driveshaft can spin freely. Then put it into 4wd and check the driveshaft as well as both wheels. Everything should be engaged. If you turn one wheel while in 4HI with the front end off the ground, the other wheel should turn backwards or the front driveshaft should spin.

 

I have the electronic 4wd so not sure if jacking it up will work as I think the vehicle needs to be in motion to engage correct? the "plug" to add more fluid is pretty rusty any tricks for getting this off and what would work the best all I have on hand is wd40 and a 1/2 ratchet