Searay transom Questions?

[jwtexas]

I have a 1979 17'Searay with the 165 mercruiser I/O . About a year ago, the engine coupler went out. I had it replaced. Then, about 2 weeks ago it failed on me again. This time, I took it to a different boat mechanic. He told me that he thought I had a rotten transom, which was causing undo stress on the coupler. Now, at first I believed him until I went to pick it up. This boat has a one piece top which has never been removed. Also, when asked about how he determined this, he said he just pushed down on the outdrive and could see the trasnom "flex". He didn't remove the motor or anything else to check. I tried this and didn't see any flex. I'm going to remove the motor b/c I have to in order to replace the coupler. But how can I check the transom without tearing my boat apart? Is there some way to check once the motor is removed? Can I cut a hole on the inner fiberglass skin (I was thinking of maybe a 4" hole) and use a flash light and a knife to kind of test the wood? I got a strong feeling after dealing with this mechanic that he didn't want to waste his time on my "old boat". He tried to sell me another one while I was there!! Please, let me know what you guys think. I kind of lost here. Also, how do I know that the first mechanic properly aligned the motor and outdrive?