Aside from what I mentioned on the owners group page, I would check the transmissions. With the engines off make sure when you put it in reverse that the props lock immediately and when under power, there is no obvious slippage. This, of course, is most easily elevated underway.
Engines in these boat varied but all to my knowledge used saildrives - probably ZF's which are basically Hurth
transmissions mated to a drive.
I have had mixed results with Hurths. Some people feel that you don't get much more than 2000 hours out of them and that they aren't worth rebuilding. I certainly agree with the latter sentiment.
You might also want to take engine oil
samples back with you to have them evaluated.
Good luck. It has been a great boat for us.