Well, if your cases aren't flush as they appeared in the photo above, here will be my ghetto fix.
RTV is a huge no-no on aluminum, but I think you're forced to use it in this case. All the non-hardening sealants are just too weak IMO.
So, with that said, I'd remove the cover, clean up everything again with brake cleaner, and try a light amount of RTV.
In the US, we have Permatex Ultra Grey. Not sure what's in NZ?
The key is to apply it and carefully put the cover back on ensuring the RTV doesn't get mashed unevenly.
Torque the bolts to 50-75% of final torque.
Let it sit 2 hours.
This allows a "gasket" with high durometer to be formed.
Then torque to final.
Some will balk at this, but I have lots of experience fixing leaking old Chevy V8's!
