very low stall current in geared 12V DC motor
40mA is certainly possible and seems reasonable for that little thing.

However you can also check stall current another way. Measure the coil resistance.

With no power, or anything else, attached to the motor, use your multi-meter to measure the resistance across the terminals. Turn the motor shaft very slowly (Harder to do with a high gear ratio motor) by hand, or pliers, let it stop, take a reading, repeat a number of times to find different commutation angles. Then note the lowest non-zero resistance value. 

Then, using Ohm's law.. Divide 12 by the resistance value you just measured. That will give you the stall current.

If your 40mA current is right, the resistance should be @300R.

Note: Your 40mA may be off if the shaft is locked in the wrong commutation angle. Better to let it struggle to rotate and measure the max current. However, even then, the rotor may be oscillating/vibrating over a commutation cut and the current can vary enough to give you an incorrect reading with a multi-meter.