W.W.
I have several Badger's, and have had several other types as well. The only valve failure I experienced was with a Paasche, the symptoms seem much like yours as I recall. The problem was with a swollen "O" ring, probably my fault as I had likely allowed thinner to enter the valve during cleaning. You may already know, but it's important to keep the airbrush pointing downward when cleaning, to prevent anything from entering the valve area.
It may be possible to use a little airbrush lube, or even chapstick if you have none, to help the mechanism function sufficiently. Worth a try.
If you haven't checked it out yet, I heartily recommend a look at Don's airbrush website. Just Google it that way, you'll find all kinds of info that may help you diagnose and fix your problem.
The Badger line is my favorite overall, I use all four of the 200 models, plus a 155 and 100G. For the most part they remain trouble free and reliable as a hammer, with LOT'S of use. Don't give up on it yet, once it's sorted you'll get many years of good quality service.
Please let us know how you make out with it, good luck.
Patrick