The original Universal M-25 diesel engines from Westerbeke / Universal had an obscenely poor alternator bracket design as they shipped from the factory. As long as the bracket did not fracture you could run them for a period of time without too much issue. Boats normally tied to a dock with constantly charged batteries seem to fair better. Boats that are cruised and the batteries deeply cycled seem to break these brackets more often.
The problems arise when, not if, they do fracture. When these brackets break they often puncture the oil filter and can often take out the entire timing gear case in the process.
The original bracket is also made of cast aluminum which is simply a very poor choice for driving the needed HP of an alternator. The new bracket is welded steel.
The old style bracket mounted to an ear on the timing gear case which is easy to break when an alternator bracket fails. If the timing gear cover breaks you are into a HUGE project! This engine already had the timing gear cover replaced once!! Sadly the techs who fixed it had no clue the old style bracket should have never been re-used.
Keep in mind that when, not if, this bracket fails you will be dead in the water with no engine. The belt on these engines drives your fresh water cooling pump and this is required to run the engine. No alternator not cooling....
If you have an M-18, M-25 or early M-25XP, and your alternator bracket looks like this, REPLACE IT ASAP !!!!!!
This image shows the old alternator bracket design and LOTS of belt dust....