Huh... I would think that if it leaked enough that you see it dropping on the dipstick that it was leaking fairly fast. As in, you would be seeing a puddle if you man-handled the hydraulics under pressure.
Maybe it leaks when you have a load against the hydraulics. I had a FEL fitting like that, it would not leak under its own influence, but if I put a bucket of snow in it I saw a stream start coming out. My issue was simple, I tweaked it with a wrench and never saw that leaking again.