Interesting that the trailing arms and their bushings are the same for the 135i and M3.
Found this online about a E90 M3 trailing arm failure that the owner could not remember any situation
that would have caused it. The buckling away from the fuel tank and slow progressive failure is a strong argument to leave the trailing arms stock for safety reasons.
http://www.m3post.com/forums/showthread.php?t=413117
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ER CP, Forge DV, Wagner FMIC, PE, Maddad Mid, ER Sports OC, BMS OCC, RB Check Valve, AFE intake, Cobb AP3- Stage 1+ drive, BMW SS, PS Springs, Yellow Koni external, M3 Control Arms F & R, M3 Strut Brace, M3 Sub Bushing, Rouge Toe, Dinan Camber Plate and Rear Shock Mts., E93 M3 front sway bar, Mfactory Diff, Arc 8 PSS 235/40/18-265/35/18