Just FYI...
I have cleaned literally hundreds of Electro rangefinders with a Q-Tip and a 50/50 solution of peroxide and ammonia. I have never had a problem with the beamsplitter coating coming off. Of course, be gentle with it, but I have yet to destroy one.
I tried the same thing with a Canonette QL17 GIII, and it came off with one pass... :bang:
Russ