Take a good look at the original vw crimp on connectors they are different than the garbage they sell today.
these are called "open barrel crimp  connectors" they take a special crimper.
never have seen one fail except from corrosion. Soldering the the garbage they sell today is lipstick on a pig. First rule of soldering is make a secure mechanical connection. Second rule is don't depend on solder for mechanical strength.
mike