Loose Brake Caliper W126

Hello,

Today, while driving my 126 300SD, my left front brake caliper came loose! The top bolt apparently fell out, but the bottom bolt was in place with the caliper making a grinding sound while hitting the brakes.

My question is : I usually have done my own brakes for greater than 5 yrs, however, I have been re-using the old caliper bolts, usually without locking compound, and torque them with a hand torque wrench to specs. Do I need to change the caliper bolts with every brake job (if not, how often), and should I use a locking compound (if so, what is recommended brand)? Any other advice on how to prevent this dangerous condition again?