Both of the Shoebox compressors I've had with the auto oilers have done this. It really irked me.I cleaned both of them up and took the felt wipers out. I fill my rifles straight from the Shoebox so no heavy use. I just brush on divers grease every now and then. I get no black oily residue, or any residue at all, and after over a year I still haven't had to rebuild the compressors.
Is it possible maybe an o-ring has failed on one of the pistons or is this just normal silicone oil blowby for a Shoebox? I haven't run mine yet so I don't know what normal operation is.
Do you think your guns are dieseling because of the silicone oil or the oil is doing something else to cause the velocity issues?
A few questions:Have you confirmed that this substance caused your gun problem? ie you found that stuff in the regulator, cleaned it up, and working again. It would seem to have to have a very significant amount inside the gun air tube, such that the oil would get into the inlet of the regulator. I don't think the silicone oil atomizes at this pressure or is that wrong?
Are you using the "heavy" silicone oil provided? I think it is like 1000cps. Using a thinner oil might cause more to bypass the O-rings. Now, I have been adding a few drops of silicone oil into the inlet of the SB after I have done filling a bottle (about 1 hour run time to fill guppy or 90ci). That is because the inner oring does not see much lubrication. Oil/grease has to pass thru the outer oring to get to the inner one. The inner also takes the most abuse, where the piston actually moves completely out, then back in. Outer always has contact with the piston shaft.
Are you sure it is not a mixture of water? That sounds like what I have seen in the hand pumps, as well.I would be interested in Tom's or Carol's input on this as well.
Also, normally air flows VERY slowly through the Shoebox, when you open the system and flow air very fast it will take the oil with it.