I was borrowing a friends wagon and had the same issue. Judging by your 2008 post I will suppose that you've found it by now. Since there may be others who search for same I will just mention that on my friends wagon the handle to the dipstick had broken off and all that was left was a small piece of wire (the remaining dipstick handle) protruding from what appeared to be a bolt hole on top of the valve cover. Looking at the top of the valve cover you will see several bolt heads holding the cover in place; right in the center (off to one side) one of the bolt holes should look different. That will be either the dipstick of the hole that it normally protrudes from.