Hugo,
Do you have some more pics for us ? So it will easier to look on the right place where to search for cracks.
It’s astonishing that not more members writing reaction on this thread because this is one of the most serious problems our M3W can have.
This is proved by the way MMC react by replacing the chassis.
But this doesn’t help the ones who’s having the same “weak” chassis and still need to drive around with it.
They all need to keep an eye (day by day, mile by mile) on this dangerous problem and keep the fingers crossed that nothing serious will happen.
For me it’s 100% sure the “older” chassis are build from the “wrong” type tubing material.
BUT NOBODY WILL EVER ADMIT THAT !!!!
It’s like the Covid19 virus.
You know it’s there, but you don’t know if you will get it.
The bolt-in brace is like a mouth cap.
Stay safe, stay in lockdown which means keep your M3W in your garage.