Re: can you inspect transom to ensure wood isnt rotted?
1/4" drill bit approx 1-1/2 " deep on the inside and look at the shavings ..
Dark mushy stuff = no good
Dry white(ish) stuff = good
Wet white(ish) stuff = wet transom but no rot ( still safe to use )
Drill hole seeping water = 90% chance of full blown stringer/deck/trans resto

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Fix by filling hole with 3m 5200
Moisture meters .. hmm.. Ill bet 10 bucks right now your going to show elevated readings ( most all used boats do ). Does not mean your trans is gone.
You can do a core sample with a 1" hole saw but your going to have to glass patch any core samples you make ( there is a sticky up top on how to repair core samples in the " how to " thread )

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YD.