Durst M601 focus issue
I've recently acquired a Durst M601 in a pretty grimey, but complete state. All seems to be working well except the focus adjustment which extends the bellows. The know on the right hand side is turned to raise and lower them however it just spins. It appears this knob is connected to a shaft that runs next to the right hand guide rod. There is a set screw that applies pressure to a tang which in turn applies pressure to the knob shaft (sorry but couldn't come up with another name) . It doesn't seem to matter whether the set screw is tightened fully or even removed. The focus knob just spins having no effect on the guide rod. It's as if something is worn and slipping. There is some crusted white stuff in there that could either be a lube or friction material but I can't tell which by its age. It's not even clear if the knob shaft makes contact with the guide rod as it's a little hard to see. Does anyone have any experience maintaining these enlargers and know how I can get the adjuster to grip the guide rod?