Did you try putting some baby oil on the bolt, and firing it that way?
If you haven't, try putting some baby oil on the bolt (just a little) and firing your marker that way for a while. I'm sure that will fix your problem. That DP40 lube causes the o-rings to swell, and they squeeze your bolt, and hold it in place.
Just do yourself a favor, and try the baby oil. If it works, you'll save yourself a ton of time, because sending your marker back to DP can take weeks. If it doesn't work, then you are only out a few cents worth of baby oil.