Distributor filling itself with oil

I'm floored .
Looking at how that vac advance is mounted thru the case, with the vac canister remote from the body, with a rod thru the the case, I couldn't imagine how vacuum could be created inside the body, never mind how wet those things get inside, while off-roading, absolutely amazing .
I wouldn't think it'd take much vacuum. That small amount, coupled with a "little" normal engine blowby and there you go.