You might not like my answer. For my car, I removed all the factory seam sealer, which doesn't work worth a damn anyway. Then wire brush the rust and brush on Eastwood Rust Encapsulator. Within the top coat time, spray some primer on the rust encapsulator. Use urethane seam sealer to reseal the seams. Unlike the factory stuff, the urethane WILL stick. That's what they use to glue windshields in place. Then use a puff can of body color touch-up paint.
You can order a factory color in a spray can online.
The easier solutions NEVER worked for me - not in the long term, anyway.
