[special-K]

I take a screw driver and hammer to chisel it all out.It`s hard and pops tight off.If you have a drill,go buy a 3M abrasive wheel at a hardware store.Those squiggley plastic fiber thingies.If no drill take coarse sandpaper to it.I like Permatex Rust Treatment.Napa has it in spray on.Let it set until the next day and put the seam sealer on.I get that at Napa,too.It`s a cartridge for a caulk gun.just lay a nice fat bead across there from end to end.I take an acid brush like plumbers use for flux,put some thinner in a spray can cap,and keep wetting the brush while you spread the sealer across the entire area.It will take a long time to set up.The thicker the longer.I wouldn`t re-prime until it gets pretty firm to touch.Could take days.
You may find you have pinholes rusted through which is where your water id coming from.Let the sealer take care of that.If you were doing a restoration I`d say break out the welder.But,the sealer will do the job.You`ve now stabilized the source of the problem.It takes a leak for a long time to rot the header panel(area above the windshield inside).The water wants to run down and gets caught in your cowl or leaks down to the kick panel area.You western guys have solid bottoms compared to us eastern guys(I`m talkin`trucks here),but the sun can bake out those gutters and cause what you have.It seems that it`s just starting to be a problem in recent years.I go after the bad sealer in trucks I bring back as soon as I get them.