What is your storage/parking situation? If you are in an enclosed, unheated and uninsulated space with no vapor barrier you will get a lot of condensation as the air starts warming relative to the surfaces. This is especially an issue with a barn/garage that is on compacted dirt or gravel - a vehicle in that space will get soaked from below from the moisture coming up from the ground. This applies to interior surfaces that are vented too, like your valve covers. Starting it up and letting it get fully hot should cook off the moisture if this is where it is coming from.