"Hill Stopper" Clutch

My 86 GL had it, My 90 Legacy has it and my 04 Forester has it. It's a valve set up that holds the brake fluid pressure in the system when on inclines if the clutch is depressed, and releases the pressure when you engage the clutch. The 86 had to have the valve replaced (scrap yard) at about 230,000km. It still worked but developed a leak.

Your mother was absolutely correct. The hill stopper was a great selling point in the days when many people still wanted a stick shift.