tank tee

My water system recently developed a pinhole leak in the pipe from the pressure tank tee to the pressure tank. The tank is an Amtrol WX-203 and is over 20 years old, so I've decided to replace it with an identical one, along with the associated fittings. I've attached a picture. The gray...

I could use an expert's help. My Well-X-Trol (WX-251) is fine, but the drain on the tank tee is leaking, (and the packing nut is tightened all the way in). I was going to replace just the drain on the tank tee, but all of the plumbing is corroded, and I figured as long as I was going to drain...