A non-oem solution could allow you to run a stiffer, more agressive suspension setup and tires than the oem solution without damage, providing a performance benefit over the oem solution. In that case, someone with the oem solution would potentially have to do a points modification to get their car to the same stiffness level that would allow the suspension/tire mods. It doesn't appear that cost plays into any decisions of this type. If it did, modifications for my car would be 1/10 the point value in the rules because the parts cost 10x as much. But, that's the price you pay for having a BMW (or Ferrari in my case).
I see your point, if this was in fact relevant to running a stiffer suspension system. There is no rhyme or reason for the sub frame failures as it is for ALL E46 chassis'. Half of the failures were never raced a day in their lives.
Given that the settlement presented specifically excludes cars that have been modified for any reason, I think the stiffer suspension argument applies. The settlement is pretty much saying that if you alter the suspension in any way this could happen, and that BMW is not liable for that, and the settlement group agreed to that term. There is no federal TSB for this as far as I'm aware. I'll go back to my original statement that almost every BMW that is tracked heavily has subframe re-inforcement plates similar to the ones that Turner sells because they all have issues with cracking subframes, motor mount points, and sway bar mounts with stiff suspensions. If the plates resolve a known weak point in the car and now allow you to run 1300# springs, as opposed to a competitor that can only run 500# springs, I would say you've gained an advantage. You would both be taking spring points, but the max stiffness of the spring you can run is really dependent on what the car can handle. Maybe having a super stiff spring isn't the best setup for you and your car, but there are some drivers that can make a really stiff car perform wonderfully where it would be frightening for others.
I think another important point that I hope Greg is looking into further, is, has there ever been a catastrophic crash/failure from this happening? My thought is no, I've never heard of an accident happening because of this. It usually starts to tear and a really bad clunking noise develops and maybe you see some wear tire wear from your alignment shifting. It isn't like you are going to be coming down the front straight at 140 and bam there goes your rear subframe and everything else like somebody had it hooked up to a chain, hollywood style... It isn't like the lotus problem where a link breaking renders the steering wheel completely useless and you are just along for the ride until you can get the car to stop. If your car is developing this problem, proper maintenance and inspection should prevent any accident from occurring as a result.
Dew-e, you seem to be arguing against this being a free mod (not sure what your stake in this is) but the points you raise don't seem to be helping your argument. You state that this is a known issue, and is worse on cars with modified springs/suspension and sticky tires...which is basically anyone who tracks their car. That is exactly why I'm raising the issue! Regardless, the problem occured on cars that were never modified and never saw the track. The concern about spring rates is puzzling to me. If there was a massive performance gain to be had from running 1300# springs, the rules would have been written that way. But they aren't. Every chassis has its limits with how stiff you can set it up, it just so happens that on E46s they were severly limited when they rolled off the assembly line.
To keep things simple. I want my car to last and don't want to spend thousands of dollars to make it last when there is a known issue surrounding the subframe and a cheap and relatively easy solution to make it last exists. There is no performance advantage with this modification. There is no unintended performance advantage. There is also the safety issue which I have raised. If the subframe lets go the car will not spontaneously combust but if you're driving on the limit in a corner it could be enough to take you off the track into a wall...even if there is no documented incidents its about being proactive, not reactive.