Last fall on a trip up to Ft. Collins.... I saw the weather maps, shouldn't have hit the road, but I did anyways. Just about the harriest trip of my life. Snow drifts, slush, wind, my wheel wells were solid ice from all the way up around the filler neck to clear up in behind the bumper with about two inches of clearance around the tires. Should have taken pictures. Solid! I wouldn't have even been able to see a CAT filter up in there. I'm serious when I say that I just may stick a filter up in the corner of the pickup box. I'm not planning on putting a toolbox there. Heck, even if I did, I would put it inside the tool box.
Yeh I should have added that the clever addition of a lift pump simply puts the fuel back to about atmospheric pressure and the entrained air does not float to the top in the filters. It simply stays dispersed in the fuel and passes right on through to the injectors.
Believe it or not, but cavitation bubbles can come pretty close to being a pretty good vacuum, ie, nearly nothing in them. However, as you note it's usually some of the fluid itself in a particular vapor phase based on "how good" the vacuum is. When those little puppies collapse they do so at supersonic speeds. What you have then is this really, really high velocity liquid etching away at whatever surface is nearby.
I was really surprised to hear that GM (or Bosch) actually changed the material in the injectors beginning in about mid '01 production. Good news for some of us. They must have been running some pretty serious life studies around the time the Duramax was introduced to realize so quickly they needed to harden up the parts. Unfortunately, they were probably doing this with super clean fuel or by now we would have seen some changes with that OEM Racor. If GM is losing a lot of $ doing injector replacements under warantee, you can bet that a change in that OEM filter will be coming pretty quickly.
Come on Racor, the data is already in (here at least)! We need a better filter