Yes you need it. As well as being an anode, it corrects for steering torque produced by the propeller. Without the tab the steering will be pulling one way all the time....
Sorry to be so dense on this, but is this something specific to the motor or are they universal and pretty much one size fits all? If so, then I'll try to pick one up local.
Specific to the motor.
there may be motors that use the same one.
take serial number of motor, to a merc dealer or whoever.
It also helps to prevent galvanic reaction/corrosion.
