87 International S-1754 PTO problems

Here are a couple pictures of the hoses and Pump setup. If you look closely, on the top of the piston where the hose connects, there is a threaded plug. I fear that if I take that out, the bed will lose pressure and drop. When the bed is fully down, there isn't much room to access it. I figured I'd put a 6x6 in there in such a way so it can't slip out. That would give me more room to work on it.

 

This shows the bed raised as high as it will go right now. The PTO engages & the pump works, but my feeling is, it's low on fluid. The pump leaks, & it loses pressure (verified by dump bed wont stay up) but since there is no tank I am assuming I have to open that plug in the block that sits on the piton as seen in the second picture. Is there a better way? Since it will be used so infrequently, it doesn't make sense to add a tank, just looking to top off the fluid. Any idea what flavor fluid might be in here? The puddle under the pump is black, so that rules out tranny fluid.

 

Here are pics of the top of the cylinder, that's as far as I can get it to go up. Like I said I am guessing it's lo on fluid. I still have no idea where to put the fluid in.

 

Here are some more pictures, I took the plug out on top of the block seen in the lower picture, there was a spring inside, I put some fluid in there til it overflowed, put the plug back in, and got the cylinder to go up a little more. I then took out what looked like a bleeder or a grease zerk (vice grips) up towards where the piston comes out. A little air hiss, so I left it loose. Then tried the lower plug with spring again and got some air, and only a little bit of fluid went in. Piston didn't go up any higher. I can't seem to figure out where the fluid goes in, nor how to get the piston to go any higher...

 

I don't see a fill plug, am I missing something? No reservoir tank, no fill on end of cylinder, and can't get fluid to go in the plug at the bottom (pic in last post). Am I supposed to put fluid in the little breather with the vice grips on it?