Sir,
One drop on the four sides...top, side, bottom, side is plenty!!! Using more may cause the cracking that you read about....
One drop ...that is it...and not a huge drop..one small drop...then put a little pressure on it from the inside of the insert...let dry a second or two..then to the next area and the next drop...
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"A conservative is a man with two perfectly good legs who, however, has never learned how to walk forward." - FDR