The lift cylinder has a leather chevron style packing below that gland nut. Tighten the nut and it should stop or all but stop. I have seen some come from the factory pretty loose. The leather will also shrink after it sits and drys out, this can happen between the time it is manufactured and when it finaly gets installed on your truck. I have also had some that never stop leaking, but Curtis should give you no problem replacing it.
I noticed a leak in my lift cylinder last night, was going to call around for a replacement tomorrow, but took the advise, and tightened the nut, No LeakTry tightening the round nut at the top of the piston. They require a spanner tool to do it properly, but a pair of Channel Locks will work. Just snug it and check it, if you make it too tight, the piston won't want to drop and you'll wear out the seal faster.