I am having problems starting the 90 lately. It seems that the key core is going bad and every time I start it, the key returns to the off position. Not all the way back, just enough to turn the truck off. If I turn the key very slow and let it come back slow it will stay on. If I just crank her and let go the key returns to far. Any one have this problem before? Could it be another problem and not the key core, can I replace the core myself?