Fireplow:
How many miles on your D?? Sounds like you might be in the market fro a new set of plug wires.
My 04 only has 57k on it, and runs fine in wet weather. If you think about it, those wires live in a pretty harsh environment.
Be VERY CAREFUL spraying water on your engine. Too much in the wrong place especially if its hot can quickly equate to a large repair bill.
Don