If the seals in the jack itself are leaking they will have to be replaced and removal of the jack is needed. If the hose is leaking it also will have to be replaced. Not knowing your level of skill at mechanical and hydraulic it is impossible to say how difficult a task may be.
Once the jack is off they can be rebuilt; the hoses can be made up at a hydraulic supply shop most of the time. Many time the cost of rebuilding a jack can be as much as a new one unless you find a local shop that can do it and save the cost of shipping it out.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7