82 300DT - Need trans guidance?!

[g. faircloth]

Thanks for looking in -- My son ran this 300 low on fluid, though I haven't found the leak yet? I had to add 4 quarts but the trans had already started slipping and lost reverse. It has no Low Gear or Reverse but will go slowly in Drive. I'd like to try and see if I can fix this but where to start? I see a wire leading to back of trans which is nearly sliced in two in several spots and using a voltage tester shows no sign of life? Is there a few things to try before opening up trans - I've read the B2 Bore is a common problem but is that a possibility to try in this situation? Any advice is greatly appreciated - I'm not ready to give up on this car quite yet! - (with the forums help!!)