Howdy.

I am in the middle of repairing a classic vacuum pump leak on a 2012 Passat with a 2.5 L gas engine (B7). It is going well, but I ran into an issue.

This repair requires removing the gear position sensor to get access to the pump. The sensor is held down by two bolts and a hand tight nut on top of a locking ring. Beneath that lock rink is a flat black washer of some kind. When I went to remove that black washer, it flaked and disintegrated into a hundred pieces. What material is that washer and what is its purpose? More importantly, can I skip it when I re-assemble, and if not, what should I replace it with? I haven't been able to find a VW part number for it. My guess is that this is some kind of adhesive lock ring. That nut is only hand tight.

Attached a photo, but you can see it better in these youtube videos. Links are positioned at the moment it becomes visible.

Thanks
H