Along with removing the starter, disconnect the front drive line. That gives about the best visibility and access.
While you are under the truck, wipe everything dry then pump the primer button a few times, watching for the leak. I found mine that way. If it turns out to be a hose, which is most likely, you can get a set of replacement hoses from Foster Truck in Tacoma, WA. Two 2' lengths of hose and 4 clamps for about $25
It takes two sizes, 5/16" and 3/8"