You can buy a seal kit for the jack. You can also take it to a shop that does hydraulic repairs, will be much cheaper then an RV place. Hydraulic repair shop won't need the kit. Will probably need to take the jack off yourself. An RV service shop will probably just want to sell you a new jack because they don't have anyone qualified to repair the jack. Click On the link below and scroll down until you see the files for Seal Replacement of Hydraulic Leaving Leg, download the procedure.
1999 35 ft. Dolphin 5350, F53, Banks System, 5 Stars Tune, Air Lift Air Bags, Koni Shocks, Blue OX TruCenter, TigerTrak track bars F&R, Roadmaster 1-3/4" rear auxiliary sway bar, 2004 F450 Lariat Pickup 6.0 Diesel Crew Cab DRW, 4X4, GVWR 15,000, Front GAWR 6,000, Rear GAWR 11,000, GCWR 26,000,1994 36ft Avion 5er, GVWR 13,700, 2,740 Pin Weight.