A lot of Soldering is using the right equipment. Using a POS iron from walmart will cause you to do shotty work. I use a Weller Iron & station, and soldering is actually fun for me if ya lived close by i would fix it for ya

In any case I would never solder on the ESC b/c that would void the warranty. You do know those 6.5mm bullets disconnect from the ESC right? Replacing that wire means you will have to resolder the end on the deans and the 6.5mm bullet on the ESC end.