I've got a Roush 427 Windsor stroker 505hp 520ft. lbs. Twice I've broken 4th gear in my RBT, 7 years ago and now. Both times during track days. Once on a downshift, once on upshift. First time all the gear teeth were stripped off, this time just one broken tooth. Reading old posts someone said the input shaft can deflect at high speed and 4th gear is vulnerable being in the middle between bearing supports. Also the weakness of helical cut vs straight cut gears. I realize this is a 50 year old design and perhaps the reason for the T44 development for 500hp engines. Anyone else have this happen especially during track use?