Frank, thank you for the link. That really turned on a light. That makes perfect since now, that coupling would have a flared fitting at the supply line. Apparently the end with the straight tread, threads into the housing and the nut acts like a lock nut but with the O ring sealing it.
Eric, thanks for your input. That's a good idea, I will look along the supply line for a shut off. But I got a feeling there isn't going to be one. Last thing I want is 10 gallons of fluid on the ground.
I had to replace the fluid about two years ago. I had it in the shop to replace the engine compressor. It got really cold here in Denver and when they started it to put in the shop it blew out the hydraulic cooler. Unexpected repair. If I remember correctly the fluid was about $300. I found a new radiator because they could not repair the old one. That was over a$1000. Again, thank you for your help. I will let you know how it turns out.