These are quite well built boats; Pearson brothers really knew their business.
1. Rotted compression post base - There is a wooden wedge driven under the compression post with the bottom of the post and wedge in the bilge .... allows rot and movement of the compression post AND shifting of the bulkhead that supports the mast base.
If there is rot, the head door hardware wont line up and the door may not close or may bind when closing. An easy fix for a DIYer but very hard to realign the bulkhead and head door if the 'shifting' has already occurred.
2. leakey stancheon bases. Pearson, due to the relative thin-ness of the deck top layer, used a rubber gasket to seal the stancheons to the deck. These ALWAYS leak and water will migrate into the core. Look for radial or long 'spider cracks' emanating from the stancheon bases .... a royal PITA to dig out the rotted deck core, fill with epoxy 'mush', etc. If the rot has spread more than a few inches from the stancheon bases .... can be a 'problem' in repairing
3. Loose rudder shaft bearings .... very common. Replacement bearings available from D&R Marine (Marblehead MA). Dig a pit under the rudder, drop/remove the rudder and replace bearings, etc. Do this every 3-5 years.
4. These boats have 'floppy' hulls that easily distort/deform when placed on jackstands. Simple rule: NO blocking under the keel at the aft end .... draw an imaginary line from where the aft end of the keel joins the hull and translate this line all the way to bottom of the keel ...... NOTHING goes under the keel aft of this 'line'. You'll also need a vee poppit on the bow and one between the rudder and the propeller. Dont do this and you will get sometimes SEVERE hull deformation when the boat is blocked on the hard.
P30s are GREAT boats and if set up well will have very little helm imbalance ... a pleasure to sail, and with only finger tip pressure on the tiller.