the rear differential im my 1981 dodge 2500 van is whining. leaking grease out the front bearing...........does sound terminal?

Diffs can whine if they get water in them or they simply just need an oil change or there running low on oil. Unscrew the top bolt on the diff and see if you can see any fluid, the oil level should be close to the top, or if you put your finger in the hole and check the cleanliness of the oil and it's looking dark, could be an indication that's it's time for an oil change. It would take bout a liter of hypiod gear oil for a change.