A drop of crosman Pelgun oil on the tip of the CO2 powerlets has been suggested by alot of people. I use just a dab of spray silicon once in awhile, then spray the outside of the gun and wipe off the excess with a towel before storage. Another one I've heard used is air tool oil or Marvel Mystery Oil...the red stuff. I've heard conflicting reports saying that Crosman CO2 powerlets have some oil in them to begin with, never tested that theory on my own though. Just remember most household lubricants make better cleaners than lubricants, like WD40 is GREAT for taking off sticker residue, but a terrible lubricant...I use it primarily as a cleaner. 3in1 is another one I would call a cleaner. The biggest thing I think is to NOT use too much of anything, just a drop every other fill or so, then a spray and wipe down before storage. A little silicone oil does me just right, and I'll keep using it until something breaks.
Dan