I'm still new the trade and recently started brazing. I was told reversing valve is one of the most difficult parts to replace when it comes to brazing. one of the reasons would be because the reversing valve can over heat while installing it. One tech mention thermal block helps. Also heard an old timer mention wraping the valve in a cold wet towel which makes sense. Just wanted to know if any one has used the gel or still uses it or what brands work better than others. Thanks for your help.