When my gage stepper motors were bad they all went down to zero. I first sign of trouble was the oil gauge and it read about 80 too. Within a week the gauge would point all over the place... it even pointed at the little picture of the oil can. Like Eagle said, replaced all the stepper motors while you're in there. The guy on ebay lowered his price for a set of 6. Check them out here...
http://cgi.ebay.com/ebaymotors/6-20...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
With the soldering iron and other equipment I have at work it was a piece of cake. If you're worried about doing it I'm willing to fix it for you for nothing, just send me the parts and pay for shipping both ways.