Hello Randy (VintageUSADrum) and Welcome to the forum!
In regards to the knob on the Zoomatic strainer, this has always been the weak spot! The sad news is that the knob is a press-fit. Once it comes off, that's pretty much it. I've had luck in the past with using a Slingerland muffler knob, the larger version, and slightly drilling out the hole so I can tap the knob onto the shaft. I also have a Sound King snare, with Zoomatic strainer, that uses a nice chromed knob for a guitar volume control! Looks great, too, as it has a beautiful pearl inset! These knobs attach with a small allen screw. The last option, and expensive, is to send your Zoomatic to Jim Petty for a complete rebuild, which includes a new knob. I believe it's about $100. Jim does great work! Here's a link... www.jp2creations.com
Just click the "parts" link and then "Slingerland Zoomatic Strainer" link. You'll see the knobs in question.
Oh, and what did you mean by "the bad on the butt plate is missing"?
Good luck!
-Mark