Technical Mk11 2.0 diesel fuel filter leak

[Peterg]

Hi Guys have any of you ever experienced a leak from the fuel filter water drain screw before. I have replaced the main seal on the filter and that is dry. The leak is coming from the white water drain off screw unit which has the white spongy rubber type washer on the end of the threads to seal as the fluid runs down a channell groove in the tapered threads. I have tried wrapping the threads in ptfe tape but it still drips.

ps this appeared to coincide with me disconnecting the auxillary engine heater if that has any significance.

Any ideas much obliged.

Regards
Pete