I have a 78 1/2 ton 4x4 with a 460 and I started leaking fluid around the pressure line where it goes into the reservoir. There is a fitting that goes into the reservoir then the line has a fitting on it that screws into the fitting the goes into the reservoir. The fitting on the hose is the one that is leaking.

I'm a shade tree mechanic at best, but for some reason I can't get the fitting that screws into the reservoir to screw back in. It came out no problem and the threads are fine, but it won't go.

If I take my finger and push up into the reservoir hole I could feel something that felt like a small cylinder that was spring loaded. After several attempts this weekend to get the fitting threaded back in the reservoir this small cylinder just fell out. I simply pushed it back in and it went in and stayed and still feels as though it has a spring behind it.

So my question is why the hell won't this thing thread back in and what is the piece that fell out?

Thanks in advance for any help