Cap,
If you can afford the Mark II Model (started 1987) you will find a more updated vessel (interior, wiring, traveler, wing keel, etc, etc). Plenty on the market. For information on the 30 go to: International Catalina 30 Association website. You can download just about everything on the 30 series, owners manual, specifications for each Model, sales brochures, upgrades, etc. Its a wonderful source for the 30 owner. Yes, compression post collapse, rusting non-stainless keel bolts, are just a few of the items you have to be aware of when buying an older Catalina 30. The wooden block under the compression which will rot over time has been replaced with an aluminum unit in the 1988 model and onward. The post will subside under the mast due to the rot and you will notice a subsidence in the deck at the mast base. You can use the head door jam as an indicator as well, but the removal and replacement of the post support in the bilge at the bulkhead is timely and costly because it requires removal of the mast and should be done in the yard. The survey will certainly reveal this needed repair as too the rusted keel bolts which leads to the leeching of rust thru the fairing material around the keel, thus revealing the infamous "catalina smile". This can be costly as well. The newer models (Mark II) use the stainless bolts.
Good luck
Bob
1988 Mark II