The wear mark on the pin is probably fine. After a while the pin will start to waller out the holes in the much softer cast iron carrier. As soon as any play develops, it escalates quickly.
Get some fresh 3/32" E7018 AC and bake it in the oven for half an hour @ like 300degrees, and use the appropriate polarity (DCEP I believe) should weld very well.
HPTuner devices along with almost everything else (that's still currently sold/used) has support for 64 bit hardware drivers and Win7, or will very soon. You can also generally run in XP compatability mode as admin and get older software to work.
Cycling oxygen sensors are a requirement for closed loop operation. There is generally another parameter in the tuning establishing closed loop countdown vs engine temp. (longer warmup countdown when engine is cold)
Oxygen sensors do not cycle until they are warmed up.
Oxygen sensors can cycle...
Shawn, what is it that you are trying to fix? Ive had pretty good luck with Durafix aluminum brazing rods as long as the application doesnt need to hold pressure or be structurally solid.