Handbrake doesn't touch the wall of the trailer. Saws set in on an angle- about 10" from the power head to the wall.
I'll have to look when I get back to the office, but as I recall, three of the five were close, and two in opposite directions of production. Four of the five were purchased at the same time and will be 4 years old this May, and the 5th saw was purchased almost two years ago.
As far as handbrake use/training...
general rule: walking more than 10ft between cuts, set your brake. Moving more than 50ft between trees, kill your saw.
crews are shown the spool-down of a chain and when to, and not to set their brake.
Something dumb like being seen setting the brake with the palm of your hand (except in particular circumstances) puts you on swamper duty for awhile. Training is thumb-wrap never leaves handlebar and it's a roll of the wrist to set the brake.
I'm definitely open to the fact that operator miss-use has a potentially big factor to play here, but the idea that five saws, representing a moderate timeline of production (but not great), all fail in the same spot within a two-month period. My guess is that we'd have found all five saws with the stress fracture at the same time if I knew to be looking for it.
I'll keep you posted. Left a voice mail and another email with Stihl today.