There isn't a cylinder leak because the oil puddle would be there, not over in the tank area (these two areas are separated). Please note, this is happening on three machines, so it's a design flaw or a service technician mistake before me. Older model WAV50-118 would start to leak on the lowering valve solenoid, but that's after 15 years. This seems not to be the case on this three machines. I've also taken out the hydraulic unit from the tank, changed the o-ring and that also didn't change anything.

I've only notice that the sponge in the tank cap is completely soaked and the top of the tank is wet. So I'm thinking that there is a lot of hydraulic oil mist which drips from the cap.

When I first arrived on the machine there was a lot of oil and actually I found a rag from previous technician.