2 years .... you may have to chop some roots off those jacks before you can swap em out! No worries mechanically about the swap as it is a simple task. The cylinders will be self bleeding once you cycle them fully a few times. If you didn't get new fittings (really not needed), I'd be sure and replace the orings on them before you install them on the new cylinders.
Just for curiosity, once youíve replaced those jacks, if you take off one of the top plates to see where the leak is coming from, a photo would help see where and what is causing the leak. Iím thinking there are a couple of o-rings under that top plate.
Bob & Becky
2012 Chevy 2500HD D/A CC 4WD