Lucky might not want to do the carbs - see his earlier post on the subject. Rick G. might do them or I've been tossing around the idea of picking up a bit of the slack and do a couple sets per year. Let us know how the other methods work.
For the carbs, you might try running a carb cleaner through the system. ?Pour it in the tank - assuming it isn't Kreem lined - and go for a ride. ?There's a slightly more involved method explained somewhere in the recent past, about a month or two back as I remember.
If that doesn't work, there's no rebuild kit for the '82 carbs. ?Most likely, you can get away with giving them a good cleaning in Berryman's carb cleaner - I think it's called either Chemtool or B-12. ?It comes in a large can, about gallon size and you dip all metal parts - NO RUBBER!!! (Berryman's will eat it.) ?You may have to make a new set of float bowl gaskets. ?I've done mine twice (Let it sit too long without Sta-Bil) and the bike runs teriffic now. ?You'll probably get more help from others with the carbs. ?Also, check Lucky's Resource site for a way to make a manometer for very little $$. ?Synchronizing the carbs after cleaning really smooths things out and gives you noticeable power gains.
The horn interference problem might be solved by carefully bending the horn mount back (toward the frame). ?Which fairing do you have? ?I had a "shark" fairing on mine and had a similar problem. ?A little tweak and no more squashed horn.
Which hole does the coolant leak from? ?If its near where the hoses attach from the radiator, your water pump needs resealing. ?There is a reseal kit for it available from Yamaha. ?Also, make sure you use non-silicate antifreeze. ?Normal auto stuff eats the seals.
How new are your tires? ?First, inflate the tire to 35psi. ?Then,use some soapy water to check the valve core. ?Next, run a the soapy water around the rim where the tire meets. ?Any leaks in these areas will show up with bubbles. ?If those tests are negative, use the soapy water on the tread and locate the hole.
If the leak is in the valve core, try tightening it or better yet, replace it - they're cheap and readily available at any auto parts store.
If the leak is around the rim - a bead leak - you will have to deflate the tire and separate it from the rim. ?Make sure to mark the tire and rim so you can put it back together without significant change to the balance. ?You don't need to remove the tire entirely, just get it loose from the rim. ?Take a small wire brush - preferably brass like the ones used to clean golf clubs - and clean the rim. ?Then take some fine emery paper and give it a good final smoothing. ?Reinflate the tire to your desired psi.
The leak could also be through the wheel itself. ?It's rare but not unheard of. ?The only recommended repair for that is a tube
If you need to reseat the bead, install a tube or fix a hole in the tire, you might want to leave that to a professional. ?If you're going to replace the tire due to age, weather checking or wear, check the valve area and wheel just to be sure those are not leaking. ?Replacing tires yourself is doable but not easy. ?M/C tires are very stiff.
Hope this helps and wasn't too long. ?You know lawyers - Why use one word when many will do suffice!

Good luck and happy riding!