I could have posed this question, except my Willard 36 was sitting for over 10-years. I don't know how many of these were result of sitting or just failed. I needed to get boat prepped to head from San Francisco to Ensenada MX, a trek of 500 nms. Here's some items.
1. Diesel fuel. It didn't really smell like diesel anymore, more like linseed oil. But my old Perkins 4.236 75hp ran it just fine anyway. I would have liked to yank the old fuel but was too expensive in California.
2. Engine. I had a trusted mechanic spend some quality time replacing all hoses and belts, adjusting valves, replacing raw/fresh pumps, oil coolers, fuel filters, and heat exchanger. He found a couple hoses were nearly shot, including a hydraulic hose for my stabilizers that was within hours of blowing.
3. Pumps. Macerator was froze, as was wash-down and AC pumps. Whale Gulper on shower sump was fine as was freshwater pump/
4. Shaft packing. This starting leaking and I couldn't get it to really stop without stuffing box heating up. Needed replacing.
5. As others have mentioned, all safety gear was out of date. Older orange PFDs were rotted as they had some minor water intrusion.
6. Minor termite damage to a small section of caprail.
7. Ancient Ideal windlass worked fine. Check the chain too - if stowed wet, it could rust into a ball.
8. Ancient Yanmar single cylinder generator would not start. Was junk anyway. Replaced with Northern Lights.
9. Thru-hulls were generally in good shape. One in the forward head was OEM from 1970 and was stiff years ago and had gotten worse. This was to be removed anyway.
10. Head. I have an manual Groco Model K. Needed to be rebuilt.
11. Rot. I had some rot at the base of my mast. This was okay as it was to be removed to install a hard top. But still, it supported the radar so it had to stay for the 500 nm trip. Wasn't pretty but I stayed the mast with blocks/tackles.
12. ELectronics. Well, I used to use a PC-based nav system. Windows 98 system would not boot-up. So A/P interface was no longer operable. Workaround was manual waypoints. Not a big deal - less than a dozen waypoints for the 500 nm trip.
13. GPS. Also an ancient Garmin. It took over an hour to find itself, but it finally did.
14. Other instruments. Paddlewheel on ancient knotmeter was hopelessly fouled. VHF antenna cable was cracked and needed replacing. Antenna itself was horribly fuzzy from 20-years in the sun.
You get the idea. Trip south went fine. Didn't miss a heartbeat.
Hope your story has a happy ending. Also hope it's a less expensive ending - wasn't cheap to get Weebles back into condition.
Peter