I had/have the same problem. If you tap on the switch mechanism is usually comes on. I took it all apart and tried to lube the switch itself with limited success. Only the Germans could come up with a switch design that is as complex as this one. The design is virtually guaranteed to hang up eventually.
I did discover a quick way to check the bulb. If you open the rear trunk, it should light up both the front and rear bulbs.
BTW, how much did you pay for the front latch switch mechanism?
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