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.
Jun 5, 2012 at 4:18 PM