Is this one of the 2 bolts that hold the starter in? If it is, it needs to be fixed properly. A helicoil is very strong and an acceptable fix. But look at it closely and compare it to the other starter bolt. I believe this is a M10 or maybe M12 bolt, and it has a 10mm allen hex head. Torque to something lime 55Nm.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.