The OE style 'plate' thing relies on proper torque to work correctly. When you tighten down the adapter nut, the edges crush and the area around the threaded adapter pinches inward. If you gorilla it, it can warp and leak like crazy. The right angle adapters are known to leak as well.

So, if yours leaks, do you go to the dealer or wherever and buy a new plate and gasket kit or do you buy the cool guy Canton part and reuse it on your next block?