Your Southwind came with a one year warranty, which is probably expired by now unless you took delivery after October 1 of 2011.
Raising a wheel off the ground should not cause damage - the jack should have plenty of capacity for that. No single corner of that coach weighs more than about 3tons and each jack should have more capacity than that.
Unless you are seeing fluid on the ground, the problem is more likely a failing valve than the jack itself. That's a fairly simple replacement. If you are seeing fluid dripping out, then see if a local hydraulic repair shop and fix it. Rv dealers and jack manufacturers either charge an arm & a leg, or simply want to replace the whole jack.