My moms 1987 Mercedes Benz 300 SDL odometer is not working, she drivers over 2,000 miles a month around the state due from being a traffic controller. shes always at work sites and has problems with rocks hitting her car and such. But i cleaned her car and the next day the odometer stopped working, i know cars speedo is off but almost five but only at higher speeds and and the cruise control has only worked once but that's the has always been that way since we bought the car. Can a rock have hit the odometer counter or does the vss also record the millage this is very important because her fuel gauge is also broken and we used the odometer and trip counter to record mileage for a fill up but now there is no way to tell. I dont want to take apart the dash unless i have too what can be checked prior to that?