The red gasket that came with my 280mm VDO unit kind of squeezed out and looked deteriorated. Ordered a new one from them ( they did charge me) and its black neoprene. Just installed it.
Maybe fortuitous then that when I fitted mine, the supplied gasket was too thick to allow the two screws that also support the cable P clips to bite. Used original much thinner gasket instead.
Richard
2018 Roadster 3.7 1966 Land Rover S2a 88 2024 Royal Enfield Guerrilla 450 1945 Guzzi Airone