A couple of years in service and many wires are already coroded right up the insulation ive seen this many times either replace the wire completely or use acid core.
its not such a big deal with houshold wires which seem to be less strands of thicker wires but in auto aplications the wires tend to be more strands of thiner wire to stand up to lots of flexing these wires will quickly become
unservicable due to corosion and you will need to replace or use an acid core
solder.
could also have something to do with the quality of the wire but i would expect many of us off griders to skimp on wire cost or recycle if we can.
also totally disagree with the automotive case they do become weaker at the joint thats a fact, but good taping or shrink wrap will aleviate that problem and you will have a joint that will outlast any crimp connection even a factory original.
main problem you have with a solder joint is flexing either side of the solder
good taping or shrink wrap to provide strain relief will aleviate that problem.
