Very simple fix. Looseness is caused by wear in the ball joint that is part of the mirror mount. Feel the bottom of the rubber boot with your fingers, and you'll feel where the tension nut is. Make a SMALL slit in the bottom of the boot, stick in the correct size socket (I can't remember what size, but I think it's about 12 mm) on a short entension and tighten it up. Boot should be OK, water won't get in , but you could put some black silicone sealer on the slit if you want to. I slit mine six years ago, and nothing has gotten in yet.