I recently finished building my EVO IX, shortly after initial engine break in, I experienced an oil leak from the timing cover.
After an exhaustive search that involved removal and install of the timing components many times over I came to realize that the leak was coming from the threaded hole that the timing belt tensioner bolt goes into.

Apparently on some but not all EVO oil pump housing this threaded hole touches the oil jacket.

I repaired this problem by using thread sealant on the affected bolt.

Beware and I hope this doesn't happen to you, this oil leak almost caused my timing belt to jump teeth on a brand new engine.