In 40 years of DIY I have accumulated various spare fittings of various ages. Yesterday I was doing a modification to cure a leak and managed to create a bigger leak! I used an old 15mm solder ring union / coupling. My uncle ( a former gas fitter) used to recommend you add a bit of extra solder to these after you see the ring of solder appear, so this is what I routinely do. As this fitting is of indeterminate age it may contain leaded or lead free solder but the stuff I added was lead free. The joint leaks and I'm wondering if it was due to a reaction between incompatible types of solder? There is a complete ring of solder at both ends. This is my first time using lead free solder as I ran out of the lead type. I now live in Croatia where they only sell end feed fittings, so that is mostly what I've used.