you should really not use stop leak. Really bad for a/c systems and, or servive equip. But if you want to cheap it, you can ditch the 134 and use HC 12A. Works about 30% better then R12 or 134A junk. 7 bucks a can, and you don't need to pull a vacuum. I know I'll get flamed for it, but it does work, and you use 40% of the original charge volume. You also get better fuel mileage since the compressor is working less. But there is one drawback. It's flammable, and people are scared of it for this reason. But I seen no incidents where it's caused any fires and or explosions when used correctly. I run it in my 85 and I have 39 degree output air with it and it never loads the engine...