Fizzy
The knob Hairy Pete refers to is a push-pull device partially obscured by the cross slide hand wheel. Can't recall if its push in for longitudinal feed or pull out as its approaching 3 decades since I drove an L series for real. Easily overlooked, especially if you have Euro Safety Neurosis full circle hand wheels. I've never met one that was less than stiff to operate. On a neglected machine they can be almost impossible to move. Best to wipe hands and knob of any oil before attempting to pull out. If your fingers slip off a right painful rap on the cross slide hand wheel is almost certain.
Stiff apron controls are almost a given with an older Harrison, especially if its not been in constant use so a day or two devoted to strip clean, re-lube and careful adjustment, where necessary, of apron and slides is well worth it. Many folk stepping up from Model Engineer size bench top machines to ex industrial or training shop ones expect the bigger machine to be rather heavier to operate and un-necessarily accept as inherent characteristics that are due to lubrication faults and general neglect.
Clive