You may or may not be aware that the E series rain gutters by themselves have a tendency to rot out. The factor filler that is bonded to the gutters separates with rain and dirt getting in and progressively rust out the gutter.
So if there are any of the original rain rutters exposed to the weather I would dig out and wire wheel that all out. I did this repair and used fiberglass (waterproof) body filler. I did not have a welder at the time and it is plenty strong.
Also, treat all the bare metal (after your repairs) before painting and I would use Por-15
Apparently, the silver has much more solids in it than the black but unless you need that the black covers great using a small touch-up sprayer.
It has a small 0.7 mm nozzle so it only needs about 35-45 PSi which can be provided by almost any compressor.
Note the paint above is UV sensitive so you might need to top coat it is it is going to be exposed to the sun.
If you get the metal clean enough (prep it the same way as above products) you can use Top Coat directly. It is very hard and not UV sensitive. Again my preferred method is to spray as the working time is very long (it is moisture sensitive and goes off faster with high humidity) but invariably you get drips with smooth as glass finish due to the lack of control dipping a brush.