The new stainless-steel block for the MixMaster Pro concrete leveling gun is an option you may want to consider. This stronger, more durable gun block was developed to prevent stripping of injector ports (which can sometimes happen with the aluminum block if the ports are over-tightened).
There are no problems with the aluminum block as long as all your crew members are trained not to over-tighten the ports. But if you would like that extra level of projection and durability, consider spending a little more for the stainless-steel option.