Warning: Use the proper eye protection when drilling to prevent metal chips from causing physical injury.
Clamp the damper in a vise horizontally with the rod completely extended.
Make an indentation on the end of the damper (a) with a center punch.
Drill a hole in the indentation on the damper using a 5 mm (3/16 in) drill bit. Gas and/or oil will escape when the drill bit penetrates the damper. Use shop towels in order to contain the escaping oil.
Remove the damper from the vise.
Hold the damper over a drain pan with the hole down. Move the rod in and out of the damper in order to drain the oil from the damper.