Leaky primary case

Any tips on refitting the primary case cover to avoid leaks. Is the gasket suppose to have multiple holes for the dowel despite the fact there is only an upper and lower dowl for the pc? I'm thinking my parts supplier sent the wrong gasket? Do you anything to help the gasket sit better? Is trimming the gasket a no-no?

Thanks

Sounds like you may have been sent the 850 Mk3 gasket, this has eleven screw holes (part number 06-5534).

The earlier chaincase had a rubber sealing ring (part number 06-0398).