0w20 is for CAFE. Other countries can use various other weights (stated in the manuals outside of the US) so why can't we?
I'm willing to bet that your manual says 0w20 "recommended" and NOT "required".
They have you chasing your tail. They should have taken into consideration that the engine is brand new before making a recommendation on an intake leak. The silicon is from gaskets and sealers from the factory. In one or two OCIs they will go away.
Anytime Blackstone gives you a fuel measurement you can pretty much double it.
With that said I recommend a Euro spec oil. I'm currently running 0w30 ESP in my K20C.
As said above the 30wt will help with the viscosity loss due to the dilution.
RECOMMENDED
Where does it say required?
They RECOMMEND 0w20 for CAFE reasons. Check an owners manual from outside of the USA. You'll be surprised what grades they RECOMMEND.