I can see there are a few different things going on. We should start a new post for each but cause we are old friends...
Pressure shooting too high. I have seen the bottle regulator do that before. The gauge might say 28psi but there may be more coming out. When the solenoid opens up there is such a rush of gas coming in that the control over shoots the target.
Leak. You really have to get that under control. It can cause the O.C. to get dirty and prefocus, cause power fluctuations, just a bunch of things that will make life difficult. You will have to forgive me cause I really don't use units when I am looking at a leak. Are you saying that 905 changes by 4 over 9 minutes? If it goes from 6 to 10, for example, that's not a big deal. 6 to 46.... not so good.
So, in the order of trouble shooting I would go like this...
First, get the laser nice and stable. Good mode, Good power, No leaks (or at least no big ones) a change in 905, 10 or less is okay. Not great, just okay. Next, double check the external alignment I have attached a couple of pictures. Notice how crisp and round the burn pattern is. 2-6 optics. While you are doing the alignment, inspect the bellows. 42k, may be showing some ware. Little corner holes are not that big of deal. Then, focus lens. Of course spots, but please also consider the aluminum dust that gets on the top side of the lens. I have discussed this before. Last, the beam purge. Its important, don't get me wrong, it just doesn't' cause that many issues unless its off or really really messed up. Keep in mind you can always plumb in nitrogen, in the name of science, and see if that makes a difference.