This may sound a bit Neanderthal mate but on jobs like that I've always used Araldite!

Just your normal two-pack stuff works wonders when the mating faces are degreased and roughened. And it stands up to all sorts of heat
too, not that that's a worry at that end of the engine as it doesn't get all that hot - not when compared to the top end, anyway.

No doubt someone will suggest a little more 21sy century though :o)

Cheers!
Rudi