Look for white salt deposits around windows, unless this was only on earlier models? I know our p55 1989 windows are terrible for leaking. Aluminium on stainless with salt water just doesn't work. The salt deposits are salt as opposed to a metal reaction but it's the bane of our life at the minute.
General things to look at are through hull valves, earthing straps on flexible coupling, corrosion of any sort around windows, deck fittings, around engines.
Engines, check that the anodes in the coolant has been regularly changed, check the exhaust for colour, any oil etc.
Check all gauges, running temperature, etc. Steering, grease pump and air pressure.
Check for vibration when running
When lifted out, check each blade of propellor and check shaft with feeler gauge. Check for prop corrosion, any copper spots? Also check continuity between anodes and props/shafts with a multimeter.
There is lots to check. I don't know of any specific problems though.