Dusty's post provided the illustration I was looking for. That little clip is hiding somewhere in the crevaces of the housing. Now I know what I am looking for. Many thanks!
After 25 years of trouble-free performance, today I turned the Mark5 on cranked up the speed and then the speed fell to its lowest point and stayed there regardless of where I turned the speed dial, I have since taken out the speed change mechanism and read that there should be something attaching ...