Another method, mentioned back in the later 1960s, was to drive the car in circles, first lh then rh, several times. On our then-new 1969 C-10, it always wanted to "bind-up"/not release on lh turns at low speeds. Popping each time it slipped, which also shook the pickup truck.
TWO types of "limited slip" differentials. The one (earlier) which is locked until it unlocks, which has springs to keep it locked-up until you go around a corner and the clutch plates need to slip, whereas the later one (governor weight controlled) is unlocked until it locks up. I'm suspecting the cone clutch limited slip would be the latter type? With the Detroit Locker being a quick and positive locking rear axle. The "locked until it unlocks" would be the most critical as to additive use, although GM later advocated use of the additive in their "unlocked until it locks" units.
Enjoy making TWO black marks!
CBODY67