Marty, Thanks for your help. I found the correct horseshoe washer, rubber, nearly closed and about 1/8" thick. Now, the question is how is it to be mounted? Thus, my quest for the exploded diagram. The truck came loose and the mounting screw under the speaker is not staying tight, thus the washer was bouncing inside the car and when I lifted the car from the track, the truck fell off. Incidentally, the car operates perfectly.