Neil, you surprise me that the worm is worn and not the gear, usually the worm is steel and the gear brass or bronze and it is the gear that wears. I have had no experience of this box but of the ones I have done on tube mills and roll formers this has always been the case. As regards the colour of the oil in the box I remember one mill that we opened to change the bearings that was the colour of oil, the mill manager when showed this said that was the colour whenit was filled, I cannot remember the name of the oil it is a number of years since I worked on roll formers etc but boy was it sticky, the gears etc were in perfect condition.
Neville.