If your bow rail mounting hardware is corroded you should consider going to
www.marinepartdepot.com (look in "Bimini Hardware") and getting some new stainless steel stuff to replace it.
I was pulling myself up onto the deck and broke one of the crappy Perko type pot metal pieces. It wasn't very expensive to replace - each part was a few cents less than $10.00. It's a little more important on mine because I cut out the front section of the rail, so there's more stress on the fittings when the rail takes a load, but it looks nice too.
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Scott, Portland, OR '85 V-20 I/O, Merc 170