So, I found a rather suspect hose for the right side track attached to the center joint:
I decided to take it off to see if I can make one at work as we have a Parker Par-Krimp machine and I have made many hoses with it for my other equipment in the past.
I got one fitting off and I was letting the oil drain into a 2.5 gallon bucket. The oil just kept coming, it wasn't going to stop. This was not just residual oil in the hose. I was forced to reconnect the hose. I noticed Hitachi uses inverted flare fittings which are not common, I am betting they are metric as well.
I don't think the oil should just be draining from tank through the swivel, nor certainly a drive motor hose. Those are pressurized via a hyd piloted valve. The only things under the swivel joint are the drive motor hoses and parking brake hoses, none of them should be gravity fed by the tank. There is no way the 100 gallons should have leaked out over the last 5 years with just a leaking center joint correct?
This issue implies something else is wrong? A main valve is cracked open and not fully closed or something?
Also, all the hoses on this machine have their original brass part number tags, they seem to be all original. Googling part numbers returns ZERO results. this is not a good sign IMO in terms of a parts nightmare this machine could be. Is this essentially a grey market machine??? Were UH machines not for the North American market?