I have used both types. Until about 2 yrs ago all I was aware about was the type that softens the seals and thus repairing the leak if this is where your problem happens to be. Being in the a/c business I was suprised to find that they started to sell a product that you could put into a residential unit that would seal a leak say in a evaporator etc... I never used the stuff and thought it might not be the best thing to put into a prisitine system but I would always ask my buddies at the parts house how the stuff was selling and what the other technician reports from the field were. I only heard positive results from them. So when my suburban dumped all of the refrigerant out on the first cold front this winter. I decided that the seal on the compressor was the culprit and decided just to rebuild the compressor with new seals. Laziness got the better hold of me, but last month it got pretty hot and I stopped by autozone just so I could get some 134 and have a couple of days of a/c before having to pull the compressor out and repair it. I noticed that they had the seal softner "Stop Leak" $10-15 a can and that they had the good stuff $25 a can. I figured what the hell, I am planning on pulling the compressor anyway, if this stuff doesn't work I will only be at a $25. loss.... Well guess what, it worked a/c is still working great. The stuff hardens when exposed to air/moisture, so what I did was purge my system with a can of 134 prior to charging. I then drove about thirty miles with the a/c on. I have been very happy with the product so far.... It even states on the can that it will fill small leaks on evaporators etc..... so give it a try.... They only thing I would be afraid of is having moisture in my system when I went to charge it, because it may clog if it comes in contact with any air/moisture? so I would purge and leave a static charge of 134 prior to the addition of this product.... hope this helps
