I have cut a section of lead pipe out to put in a new stop cock to rejoin I took the sectionto the plumbers who told me I needed 6lb 15mm cooper to lead connection (the package doesn't say lead loc is that the better make) one side seems to be okay but I have changed the side 3'x and there is still leakage it appears to be coming from both the lead connection side and the copper side HELP!! what can I do to stop this leak