Recently purchased a 1970 ford 3550 loader backhoe. One of the hydraulic hoses for the bucket curl blew my first time using it off the trailer. It was right in the middle of the hoses, and the rest didn't look great either, so I decided to replace them all. $1500 later and 10 gallons of hydraulic oil, plus 150$ in tools to make the repairs, and now I have a fitting leaking at the valve. It's leaking where the check valve threads into the valve body for the boom raise/lower. I thought maybe I didn't tighten it enough, or perhaps put a defective oring on it. I removed it, checked the threads, cleaned it, installed a new oring, and threaded it back in. It did seem like it tightened....then went loose for a turn or so, then tightened back again. I reinstalled everything and low and behold it's still pouring out from this connection. What gives? Appreciate any help you can offer.