Hey all I recently picked up a used GK 400rb it looked rough but played great and I got a smoking deal on it. The outside metal case was rough, solved that by taking it apart and painting it with krylon texture paint....looks just like new. It also is missing one knob and almost all of the gray inserts. Anyonne have any idea of what I can do to replace the knobs? I thought about getting some marshall type knobs with set screws or are all knobs threaded the same? Any ideas?