Sticky key solved!

Find diameter of balance pin hole using drill shank = 1/8"

Convert to metric (3.18mm) and use successive increments of 0.1 mm drill sizes (3.2, 3.3....) to increase hole size until keylever frees up.

Result at 3.4 mm - still less than 9/64".

Now to check out against my pipe drones and see where the wolf intervals are.

Paws