I didn't think this was very common up until recently. I had 3 tanks come back loaded with oily residue and are now shot. Im seeing your post and have talked to some others and it seems like this is becoming a bit more common. What scares me is that I have 7 tanks, my previous LDS has now went out of business and they did hydro and VIP on all of them last year. 3 out of the 7 were junk this year. The only thing I can think of is the 3 bad ones were nitrox blends so maybe that was part of the issue. Though now I am a bit worried, if this happens in the middle of the dive season, other then doing another VIP how can I ever know if I have oil or something bad in my tank from a fill?