Back in the late 70s I bought a used MG 4001 that had that “dirty ring”. One of my bandmates worked on guitars and he did a deep blue finish just on the front of the bass,taping the binding. It looked really good, but I don’t have a great picture of it. I sold it after a few years.
Front photo shows Glueglo on bass horn: https://www.rickresource.com/register/user_images/32260/2-fullsize.jpg
Back in the late 70s I bought a used MG 4001 that had that “dirty ring”. One of my bandmates worked on guitars and he did a deep blue finish just on the front of the bass,taping the binding. It looked really good, but I don’t have a great picture of it. I sold it after a few years.