[QUOTE="Rear shock towers, be sure to reinforce them as there have been noted failures from metal fatigue..
Also I haven't heard this. I know this is a problem on the E46 M3 rear shock tower, but didn't realise the E9 was susceptible?[/QUOTE]
The e46 was susceptible in stock form because the computer program BMW employed to design the e46 used German roads as a frame of reference. US roads are neither designed as well nor maintained. In and around our nation's capital, the majority of our road surfaces are rated as fair to poor (and I would bet if the Germans were rating these roads they would be rated "shitty"). As I travel around I find similar road surface quality throughout the US.
The traumas transmitted by our crappy roads are less likely to be absorbed by tire sidewalls as we move from 14" wheels to 15" wheels to 16" wheels and beyond. And lowered, sporty suspensions do not absorb those shocks as well as more compliant stock suspensions. Add to this engine modifications that also impart more stress to the vehicle while putting more power to the ground and we are putting far more stress on the structures of our cars than they were designed to handle.