My guess is that the broken parts are part of the "park mechanism" that makes sure that the wipers stop in the lowered position rather than just at random wherever they are when you turn the switch off. You might check with Jim Carter at www.oldchevytrucks.com He used to have a motor for sale. You may also call around electric motor rebuilders. Maybe that park mechanism isn't as irreplaceable as you think. I guess while they are at it, it might not be out of the question to have it converted to 12V.