I have just pulled apart the front seats I'm doing on a Series 3.
Upon inspection I have noticed fatigue cracks on the upper mounting for the back squab, on the adjustable pivot hinges.
The cracks are evident from the centre bolt of that bracket.
I doubt that a motor trimmer will notice these, unless he or she has come across these before.
NB: I have tried to post pics but photobucket is saying my account is void????
I will post my repair methods when I get some argon.