I have just spent a morning servicing the engine and replacing the little anode inside the Yanmar 1GM10 engine on Beeline (P275). It was only half eaten but the struggle to remove the cover meant it was sensible to change it while I was there. The friend who helped me was very envious of the excellent engine access we have with front and rear panels removed. Certainly it wasn't a difficult job once I knew what I was looking for. Difficulty reaching his engine on a Sadler 25 meant he hadn't change his anode in several years. The next time I saw him he told me the cylinder head on his Yanmar had been found to be porous and would cost £1000 to fix. This makes the minor cost and hassle of changing that little nugget of zinc a great bargain! I suggest if you haven't checked yours recently you put it on the list. For once I have not had to learn the hard way!
Kate