And it is in the stickies under FAQ.
22. What lube should I use?
The head engineer at DP says to use DOW 55, or products similar to it. Use DOW 55 for the ram, lpr, etc. DO NOT lube your bolt. The bolt is delrin and naturally self lubing, and lube will just make delrin expand. DOW 55 is recommended for swelling the o-rings allowing for a much better seal. DOW 33 and it's similar products such as Hater Sauce, Evil Pus, Dye Slick, Shocker Lube, Sleek, and so on, will work as well with no problems, but DOW 55 is the best.