Bofors Gun help

[tankbarrell]

From the handbook.
The right side, near the front and at the bottom, is bored and bushed to form a bearing for an outer releasing lever for the extractor, and with two holes, the front one to facilitate removing the extractor spindle, the rear one to admit a closing spring setting tool and removal of the crank shaft; the two holes are closed by a cover secured to the casing by two screws which enter a slot in the cover; the cover has lateral movement to expose the holes.

I wonder if your gun is from a non English speaking user and the M and S stand for that.