I have the same prob. A certain tank retreating right at deployment start. This tank also had head damage.
Whew thanks Dutch thought it was just me and my install. But all the same I'm sorry your experiancing this also, real frustrating.
I'm not sure of percentage but it mostly seems to happen in whatever M60 tank platoon I start out with after deployment start, it's immediate and happens on every start of every new battle right after leaving the deployment screen. I didn't think you messed with chance of mechanical breakdowns in your mods (didn't know it could be done)?
As for my secondary problem of my earlier post I'm playing everything on historical. The only cheat I allow myself is all units are visible on map, thats how I knew the Iraqis only had BMP's and troops left for the last mission so where those T-62 came from really suprised me. I really don't like using the units visable on map as I do feel it's a cheat but the AI in SABOW must have an advantage because they seem to see me with no problem no matter what foilage I'm in, the same cannot be said about me seeing them. The only time I seem to have the upper hand is at night. I can literally creep right up on any BMP or T-62 in my M60.