Your argument has been the best so far.

Given that there were only 20 gas vans delivered it seems very possible that they were simply re-purposed. Though a further question would be if these gas vans were used to kill exclusively Jews or just a means to silence enemies of the Nazi regime. I'm think it was the latter but if not, that could be compelling evidence.

I never disputed that they were used for slave labor and I assume a good portion were worked to death. However, my thought is that this practice became more common after the situation became more dire. I assume it was seen a payment for their alleged crimes, possibly just being Jew or simply a necessity to win the war. If this practice were common long before the war, I can see that being somewhat compelling evidence.

Unfortunately, I can't find the specific examples I'm thinking of but I have heard of some concentration camp guards who did do exactly what you are saying but it did sound as though many were content with their position and the situation. However, I would imagine guards who did leave haven't revealed their prior life serving the Nazi's in fear of criminal punishment.

I was completely mistaken about the mass execution of camp guards. That did only happen at Dachau and the other instances I had read about such as the execution of female guards was only after they received due process and many of which received prison reasonable prison sentences. So I was completely wrong on that point.

I don't see how killing people while leaving many witnesses would be effective at covering up their crimes. I'm pretty sure killing people was their crime. What evidence contradicts these gas chambers being used to kill typhus ridden/dying people? (Not the eye-witness testimony of people waiting in a line sending some to one line and others to another which seems to be the most common answer...)