What did you think of your Coronado? 15hp really, I thought it was limited to 10hp? You wouldn't happen to have any pictures of the engine well lying would you? I have to rebuild the engine mount as mine has rotted away.
We enjoyed it for 10 years in and out of the Bay. It appeared to be fairly well built and we never had any structural or rigging problems although we didn't race it and tried not to beat it to death. I wasn't aware of the 10HP limit. The 15 was the same physical size and weight as the 9.9 so we went with it. Most of the time we ran it about 3/4 throttle as at full throttle it seemed to just bury the stern a little more. Not sure if it was faster, it was before GPS and we didn't have any instruments. In any event, when things get really nasty and you are trying to get home, power (thrust) is good. We ran a prop with about an inch less pitch than the stock prop and it worked well. Here is one user group that may give you some info on the well:
Coronado25 : Coronado 25 Yachts
I think there used to be a Coronado 25 users group here on Sailnet but I can't find it. Good luck on your well re-build. The well has to be light years ahead of the transom mount.