Okay, for those listening, I must express why I HATE hydraulic trim tabs...
I have worked on hundreds of small boats including many C-Dory's. I personally owned hydraulic trim tabs until Lenco came out with the electric ones.
As we all know, everything is a compromise and our boats and everything in them is as well. With that statement said, the compromise to most hydraulic trim tab systems, is that they are typically mounted near the stern and somewhere under the splash well, or in a locked near or at the stern. Most of these locations are wet/moist and attract mold. The hydraulic power packs in these cases are usually subject to corrosion on their exteriors and when a leak eventually begins, you are working in a terrible location to troubleshoot and make repairs. I have worked on many 25 C-Dory's that this specific case has existed.
As a side note, when Lenco came out with the electric tabs, Bennett had a lot of negative things to say about them. As stated by others, Bennett now makes electric tabs to compete with other electric tab manufactures.
My 2 cent from past busted knuckles and mold covered arms and hands.