No, no. That's the firmware, i keep telling you...!
The tilt sensor is the thingy that looks like an open tube middle right left center. You had the colour right, though.
It houses a little ball (made by that other famous swedish factory, SKF), that should not drop out of either open end.
The orientation shown in the picture, i.e. slightly tilted, is the original one: during beta-testing, it proofed that the ball dropping out made a rather disturbing noise (intentionally, the making of a noise, else you would not know the ball had dropped: no mass shouting and switching on of lights), a ping, too much like the bell on an ice cream van.
Disturbing, not because it was too intrusive, but because it made the testers crave frozen sweets, and it did nothing to help curb the obesity problem. You can die from that, you know!
So they made the ball drop out before it would reach customers. They planned to have it do so after assembly (after all, they do care a lot about the well being of their employees), and to help that happening, they plugged both ends with axle grease. (They tried ice cream first - toffee apple flavoured - but found that caused a sharp drop in the the company restaurant's ice cream sales, a rapid growth of the waist circumference of workers at the tilt sensor assembly station, and inexplicably high costs. Also, it did not smell as nice as axle grease.)
Another problem with the original design, of course, was that you had to open the back to put the ball back in the tube again.
As such, not a big problem. But again, beta testing showed that too many testers mistook the firmware box for the tilt sensor (so you can be excused: it is not your fault. It's a design flaw).
The problem with Jürgen's back was that the axle grease worked too good, or not good enough.
The back probably was an early one, made not long after they stopped using ice cream, while the assembly station was still heating up again, or possibly even still set to ice-cream-plug conditions. The grease must have hardened, only allowing the sensor to work after the back was sold.