Just a thought, did you mean V2 gave 4's on the test track also?
This would indicate a weak channel. That would dictate a repair for me.
If you did not try it on the test track, try swapping V1 with V2 and see if the good signal moves to the other track. If it moves you have a weak channel and the TIU needs repair.
You might also get a quote from MTH on the repair and consider just buying a new TIU instead, they are available and have better signal generators in them.
