I have used Brownell's Hi Force 44 solder for years, always with excellent results. I do use the recommended Comet flux.

It seems that the soldered parts seem to have an affinity for rusting though. It seem anywhere that the Comet flux may have run or seeped to starts to rust. If the soldered area is in plain view it's generally not a problem as you see it and wipe it. If the area is hidden, it seems to get away from me and after a week or so there's quite a bit of rusting (at least more than I want, which is NONE.)

WD40, G96, Break Free, etc. will all clean and remove the rust, but it will come back. Is there something that will neutralize whatever is in the metal and keep it from rusting in the first place? I know the old trick of soaking rusty things in vinegar, would that do it?