Hi Greezy,

I've been having pretty good success with arresting rust in lapped seams with a product called 'Fluid Film'. It's a penetrating Lanolin based grease that doesn't dry out.

If you search it on EBay you'll see what's available and some of the gear used to apply it. I buy it in a gallon can and invested in a special spray gun to which I can attach various hoses and wands to reach difficult places.

I live in a high salt area and it's stopped further damage to rocker panels, the hood edge, door skin seams, and that rear quarter lap. I try to apply it yearly to winter vehicles

It's difficult to renew the failed seal on lapped seams or pinch welds in areas where you don't have complete access, and throwing paint at it may only make things worse.

I would also advise that you sand and use phosphoric acid on anything you've wire brushed before painting. Power brushing tends to glaze over the surface and makes a poor substrate for paint.

Keep at it,
Peter