This year I'm paying some extra attention to my 2 Yanmar 2GM20FC's, and
saildrives.

Propellers pulled, new zincs installed, props back on with about half the
hardware replaced.
Replace lower gear oil.
Pull exhaust elbows, chip out carbon, clean with Dremel.
Drain antifreeze.
Pull out heat exchanger coils - I found a large clump of eel grass blocking
about half the passages in one of them - now I know why that engine would
overheat when run too fast. Clean and re-installed.
Change water pump impellors.
Change fuel filters
Replace fan belt on fridge.
Replace water pump on fridge.

Still to do:
finish putting stuff back together, replace antifreeze
buff topsides
bottom paint (I have two 36 foot hulls to do!)
paint saildrives
start engines
replace plastic (strataglas) on one hardtop window
powerwash deck
launch
bend on sails
have a beer, think about installing proper raw water strainers.