Carl, Dumbdog,

Thanks for the good ideas. I think (or I fear) there may be no substitute for getting up there and ripping out the tar and indeed putting some flashing under the metal and extending out along the plastic. I was hoping of course that someone had some magic aerosol that would seal everything up and let me keep this as a fix, not a project...I'll look if a silicone spray exists. Before it gets too cold to apply anything.

Chas