How does damage to a subframe typically come about? does it happen over time or can one knock (example: hitting a curb) do enough damage that you'd need it looked at...
Yes hitting a curb won't help, nor will frivolous drifting/sliding.
Is the one in the E36 aluminium ? Is it the front or rear?
I'm a believer too from personal experience that faults at manufacture can occur then manifest themselves several years on through no fault of the owners.