I've had the case exapnd and the input shaft gather enough clearance to occaisionally whack the inside of the case. You can't miss it, it sounds like a massive "clack" and at first it only does it occaisionally. The road race guys have a case girdle that helps, but I cannot locate an example on Google. The other mod is this piece which is a rear case support.

Our vintage race Jaguars that we sponsor were breaking 5th gears approximately every 30 hours of race time. Since the addition of the Stabilzer breakage has been eliminated completely. These cars hit speeds in excess of 150MPH in 5th gear!


http://www.5speeds.com/t5.htm