What would be the best way to stop rust in a seam. I've discovered a bit of rust on the tailgate of my wifes 2003 Dakota where the outer skin wraps around to the inner panel.(like on a door skin)
I wire wheeled it, coated it with some etching prime with my airbrush, then hit it with some rattle can paint that matched pretty well (silver)
Now just a few weeks later today I noticed a bit of rust stains starting again at the seam. So I guess its coming from the inside out.

There are a few slots that would allow me to pour some sort of rust converter/killer in there just not sure what to use that'll work

Any advice or tips appreciated............thanks

I'm afraid I have bad news. You have moisture and rust somehwere in the tailgate interior, not just the seam where you tried to treat / stop it. I'd say it's doubful you will be able to kill this short of opening up the panel.

You might slow it down though if you can figure out where and how moisture is getting into the tailgate interior? A bad gasket around a lock or latch?

If you can get into the gate interior, hose the inside of the tailgate down with some rust conversion compound, let it dry for a few days and then hose the interior down with light oil. A good freind of mine used to take his drain oil, mix it with kerosene and spray it into the interior of his Chebby pickup truck doors every fall to keep the bottoms from rotting out!

Astrobuf

I will also add that rattle can paint is not a catalyst paint and will not properly seal out moisture for very long. You'll need a two-part paint with a hardener.

But if rust is underneath, it will not stop...

Your nearest PPG dealer should be able to sell you a decent phosphoric acid based rust converter. I would hose some of that stuff in there over the course of a few days, then pour some oil in there.

Get some Zero Rust from Resto Rick and follow his instructions. I think you thin it 50% and then pour it into the seam from the INSIDE. Problem solved.

Best way to kill that rust is to spray spme ospho or get some phosphoric acid and mix it 3:1 with water and spary it into the seams. This will get in there. After a few days of that wash it out, dry it out ; then prime and paint.

Anyone have past experience with this one?

http://www.krudkutter.com/mustrust.asp

I bought a small 8 0z bottle,
but have not tried it yet
and wondered if there were any tips or advice.

I have long term experience with
Naval Jelly,
is the Krud Kutter product same/better/worse?

For soaks I have tried Evapo-Rust, CLR, Lime-Away and they have all worked after a number of hours.

For rust conversion prior to paint I have tried Extend and Rust Bullet.

For spray on protection of non-rusted metal
"Synthetic EEZOX Premium Gun Care"
has worked well for me on tools in rough service
and I would recommend it for others to try

http://www.eezox.info/index.html

I've found great results with "Ospho". Available at most hardware or Automotive paint stores.

Ospho cheap and easy to use.

What is this "rust" thing of which you speak?

I have used Rustmort (SEM, I think?) a few times over the last 15 years on surface rust on floorboards & trunks. It seems to work pretty well & converts to a pretty workable surface. I did that on one trunk floor, coated it with por15 & then painted probably 10 years ago & nothing's ever come through.