84 to 87 aren't necessarily "bad years", but you should definitely keep your eyes out for potential failure points. Make sure ANY 18 you get has the reinforcement for the front crossbar (stainless anchor that has 4 bolts that bolt into the hull). It's easy to install and worth the added security. You can also install this reinforcement for the rear crossbar, but you'll have to add a porthole to gain inside access to the rear of the boat.
You definitely want to inspect the underside of the hull/deck lip at all crossbar connections (inside & outside, front & rear). If there are cracks (beyond just gelcoat), you'll be in for some repairs.
Other than that, the standard inspections hold. Check the hulls and decks for soft spots, check the aluminum for corrosion (especially the mast and front crossbar), check sails for wear, etc.
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I do know that if I get a new boat I can take my jib cars, and new main blocks with me and put the old ones back on so it's not a total loss.
Your H16 jib cars (blocks) will not work on the 18...not well. They should fit in the tracks, but they would really be the wrong block. The main blocks would probably be fine. Most people run a 7:1 on the main blocks.
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