the first step in diagnosing the cause of safety mode is to have the faults read from the car. This is your first/next/only step.
in terms of possible causes, yes, an worn out transmission can cause this, but so can low fluid, a failed sensor, a voltage problem, etc.
so, you MUST have the faults read as a first step
worst case, if the transmission is worn internally, then you will be looking at approximately £2000 to have your transmission rebuilt or a used unit fitted. Or, approx. £4500 to have a replacement from BMW fitted.
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