Welcome Sailingirl,
Off the top, I agree with everything Michael M said. That being said, you should at least look for the following:
- Check the prop shaft for any side-to-side play at the strut
- Check the rudder shaft for any side-to-side play
- In the cockpit, check the wheel for "slop" or "deadband". If there's too much, examine the steering gear, through the access panel in the floor of the cockpit, for stretched cable or worn axles in the two turning blocks.
- If you have access to a pinless moisture meter, check around the base of every stanchion and chainplate, and at the foot of the braces around the lifeline gates.
- Inside the cabin, remove the access panels and check for rust staining or watermarks around each of the 6 shroud chainplates. There have been several catastrophic chainplate failures reported.
- Look for rust staining weeping from any of the rig fasteners just above the turnbuckles.
- In the cabin, examine the condition of the mast step, and the butt of the mast, for excessive corrosion. Pearson originally built these with a mild steel step in contact with an aluminum mast in a damp bilge. A formula for corrosion, and a known design defect that many owners have had to address.
- Check that all the seacocks operate easily and smoothly.
These are just some of the big things off the top of my head. There are lots more that are less critical, but still important, such as mold/mildew and odor, hatch and port leaks, condition of sails, soft spots or delaminations on the deck, etc.
The engine is another big thing, but I'm not familiar with diesels as I have an Atomic 4, so I'll let others chime in there.
Because the 323 is a solid uncored hull, with internal ballast, there have been few reports of hull or keel problems. But do keep an eye out for blisters or paint adhesion problems.