just got my truck back from the dealer for a head gasket when i drive somewhere park it and come back i have big spots of diesel under the truck when looking under the hood i found a black plastic cap on the side of the block looks like it fell off from somewhere don't really know what it is but the cap smells of diesel and has small amout of fuel on it can anyone tell me where on the fuel system they use a small black cap appears to be like a 5/8 hex