Help! My starter fell off.

Folks, about 6 months ago my starter went bad. This is a 66 valiant, slant six 225 that we rebuilt several years back, runs pretty good now.

Anyways, about 6 months ago I got a replacement from the local parts house, and since I've had bad luck in the past buying replacement starters (sometimes they don't work!).. I was happy when it worked great.

Every couple weeks, though, the starter basically works it's way loose, the first time I figured it out the thing had almost fallen off the car.

No matter what I do to torque that sucker down (I don't want to break the mounting flanges! I might never find another starter that works, lol) the thing works it's way loose. I usually notice it when I go to start the car and it grinds my flyweel to hell.

Anyways, we're talking about the bolt (on the one side) and the nut on the other woring their way out an INCH or so to where the Starter is just hanging there.

Am I missing a washer or something, or should I just go crazy torquing it down? I'm afraid I'm going to snap the flange off.

Anybody else had that issue? I've never had another engine (or this engine with the previous starter) do that.