The rear end in my 76 Blazer is the factory originnal. It's bone stock, nothings ever been done to it. I just replaced the U-joints in the drive shaft. The 12 bolt has play in it. It clunks like a bad U-joint when I go from reverse to drive and vice-versa. It also has that feel and clunk sound when I give it gas after coasting down hill . How worried should I be ????