Steve,
The M25 owners manual should be on the downloads section of this website if you want to read that as well as Stu's info. Very easy engine to deal with. I'm new to the diesel (had the Atomic 4) and transition has been simple. If you take care of it, it will love you back.
Just did some maintenance to a dock neighbors M25 on his C30 and was able to get to everything much better than the A4.
Good luck with your purchase! You will love the Catalina 30.