The side outlet of the DV unscrews... I would remove the DV and give it a service... buy a service kit from Forge (15 ish quid) and it will )should) include the new style piston...
Unscrew the outlet and clean the DV with brake cleaner or similar... use a high temp sealant on the threads and refit... clean excess sealant off obviously... use the service kit and all should be good in the world
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