I've soldered automotive wiring for a goodly number of years and never had one fail. Crimp splices, on the other hand, corrode and break with astounding regularity. If they are going to see any wetness, I have taken to filling them with RTV before I install. I am also prety careful with the cardinal rule of soldering: Make the connection mechanically secure before you solder. With the complexity of modern car wiring, most factory manuals now devote a section to wire repair and replacement. The instructions hardly ever say to strip it back and crimp on a red butt connector. Hey, I use scotchlok taps occasionally but I'm not at all suprised if I have to redo them.
