I have a thirty five year old 2 ton that uses a similar hydraulic unit, and the ONLY time I have ever had a leak is when I refilled the reservoir with too much oil. My unit has a rubber plug in the fill hole and too high of an oil level will cause leakage until the level goes down. The leakage is caused by a rapid return of oil to the reservoir when the jack is suddenly released. With this hydraulic unit, there is only two areas prone to leakage. One is the small piston actuated by the handle and the other is the ram oil seal. I have never seen even seepage at the plugs and the release valve. Clean the hydraulic unit up with brake cleaner, mineral spirits et.al. and then remove some oil from reservoir and run the jack through up down and watch the fill hole for leakage. The manual for my jack shows the oil level as 3/16" below the fill hole but that level is too high for my jack.