1989 Odometer

This is probably a waste of time, but does anyone have the schematics of the digital odometer for a 89 GP?
I just acquired this car for free, its been floating around in my group of friends for years, and I now have it with 269,400+ miles on it.
The odometer is usually scrambled or just totally blank. It still registers correctly, and will only show up on a cold morning for about 2 minutes.
It then proceeds to scramble.
I was wondering if anyone knows of the schematics, or what causes this problem in these. I know it is rather common, but if its a simple fix, I would try to tackle it.
By the way, from what I know about this car, it has only had a small handful of repairs in its life, other than maintainence. It has definitly been a champ, considering its been beat (very hard) on all of its life. Only major problems has been transmissions (on its third junk yard AT), but you cant expect much after what its been though.
The main goal i have for this car is to hot 300K+ miles before it gets junked. Would be a lot easier with a working odometer..