Well I checked out why mine doesn't work.
I found out that there are two seat locks. One on each side of the seat.

I learnt that the seat locks work for both sides. As in the passenger's side will also unlock if I release the vacuum for the driver's side seatback.

The problem seems to be that the seatbacks do not lock as they are supposed to. Unless I manually lock the driver's side lock.
The problem is that the left lock on my driver's side seat does not work. It moves freely. It seems like it's disconnected from the vacuum element.
Could that cause my problem?

I hope it's clear enough...

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2008 BMW 335i Coupe