Can anyone tell me how to fix a leak in my air con unit without to much hassle

There you have it; The leak has to be found to be able to fix it. Sealers, additives are not the answer. We have done these for years, and pretty much have the equipment and knowledge of how. If you had a few days to spend time to spend with an A/C Technician, maybe you could learn some good information. Last word, it would probably be cheaper to take it to someone honest to fix it for you.