GM S-10 pickup Front Differential Repair

This job is a front differential on a 2000 Chevrolet S-10 4WD pickup truck. It comes in with no four wheel drive. I find that the transfer case is shifting into 4WD correctly but the front differential is not engaging the front wheels. This system uses a vacuum switch on the transfer case that is triggered by the transfer case going into 4WD, when this happens the switch on the T-case sends a vacuum signal to the front differential actuator which pulls in a diaphragm which pulls on a cable to engage a clutch fork in the front differential to engage the driving wheels. When not in 4WD, this puts less stress on the front gears as the wheels aren't driving the gears in 2WD. Unfortunately, a lot of the time, the transfer case vacuum switch will stick in the 4WD position all the time so the front wheels will be engaged all the time even in 2WD. This causes the front differential to wear pretty well and sometimes stick in between engaged and not engaged causing a noise as the gears grind. In this case, I found this to be true as I had a vacuum signal to the front axle actuator all the time. I could also see that the cable would go in out on command (me with a vacuum pump) but not engage the front wheels when pulled in. OK, I need to disassemble the front differential. I pull the vacuum switch off and sure enough it's stuck engaged. I pull the front axle engagement side apart and see that the dog and clutch gears are stripped out along with a few broken thrust washers. The main part of the diff is also heavily contaminated with black tar like fluid and needs to be disassembled also.