I'm getting ready to mount the oil pan (also using

RTV), but if my upper seal might be compromised, maybe I should go
through the painstaking task of separating the engine from
the aluminum spacer and re-sealing it, using alcohol, etc?

Paul C, Yes take it off and clean the sucker. I would say no but 
antifreeze is bad to get on anything except the inside of the
radiator and engine water passages.
A sandwich plate mount will move around a bit and you don't 
want leaks. One of the keys to using any gasketless system is to be
sure the areas are FLAT, clean and bolted up evenly. Also if 
using RTV be sure to apply a THIN EVEN FILM, not a huge bead. The
RTV that oozes out can break off and damage pumps and clog 
filters if applied too heavily.
Bill Jepson

 
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