Back to the rain gutters again. The bare metal surface inside the gutters was first cleaned out real well, then coated with rust converter, then I mixed up a batch of old PPG grey auto primer and brushed the primer in the gutters with a modelling brush. After the primer was good and dry, I used the same brush to apply the aqua colored enamel overcoat (also PPG). That can of enamel paint is probably around 25 years old but still good. Same goes for the can of hardener (PPG).
I did use the 3M Fast-N-Firm caulk in the gutters. Boy that was a huge challenge, because the tip of the caulk tube is only so long, but the top of the '55 pops up and prohibits your ability to get the angle that you want to apply the caulk. Bear in mind that the seam you want to seal with the caulk is at the far outer end where the side of the gutter turn upward. It started getting messy. I cut some cardboard trowels and used them to smooth out the caulk. I was not satisfied. Additionally, the width of the gutter changes depending upon where you are around the top, and I ended up with 3 different sizes of cardboard trowels. I finally gave up and started using my finger to smooth out the caulk. It is a lot better, but by no means the result I was hoping for. I've got a coat of the same primer over the top of the caulk now which helped a little more, and then it will get a coat of the enamel over that. I know that the first time it rains, there is gonna be little nooks and cranny's in there that will catch and hold dirt. But I am confident that the seam is well sealed, and hopeful that this will be the end of the rust up there.