I remove and replace the Welch plug if I do a carb rebuild. I've found some real surprises under them, especially with older vintage saws. Some definitely would have not run if they had not had the plug removed and cleaned under/to/from them. I don't know what the issue is, it takes about 3 minutes to do, far less time than removing and reinstalling the carb again if it needed to be done in the first place. I tap them down a bit to loosen them up and they either fall out or you can snag it with a dental pick. Clean underneath, reinstall plug and tap it gently with an appropriate sized punch until it has a tight fit. I don't use sealer and the carbs all work fine. That being said, I can't say I never used a sealer. I've had a couple older saws that gave me some fits with not running properly after a carb rebuild. I thought the problems may have stemmed from a leaky/loose Welch plug after reading here about using salers and I had not. I disassembled the carb and used nail polish as a sealer. When the problem persisted and I disassembled the carb once again, I found the polish to be soft and far to easy to remove. I felt that it would dislodge from the vibration of a running saw. In another instance, I removed a Welch plug and attempted to reuse it since I had no other to use as a replacement. I used a thin bead of JB Weld to hold it in place and act as a sealer. I tore that carb down about 3 months later because, knowing about The JB in the carb did not sit well with me over time, I wanted to remove it and replace the plug with a new one. I was surprised to find the JB soft and far to easily removed like the aforementioned nail polish. None of these saw's problems were the result of a loose or leaking plug. I'm sure there might be better/proper sealers available. I won't be using them, since I haven't found the real need to do so. Perhaps the necessity will arise in the future but, not as of yet.