I'm new to this forum and have a question concerning the best way to solder a Moen model 62320 shower valve. Do I need to remove the cartridge? I was afraid it would get too hot and melt the o-rings. How do you know how long to heat the joint before you apply solder. It seems some of my joints are turning dark and I thought maybe I was overheating the joint. Any soldering advice would be appreciated. Thanks.