Leak detection specialist with years of experience finding hidden water leaks, slab leaks, and pool leaks using non-invasive acoustic and thermal imaging technology. Happy to share trade knowledge on leak tracing and moisture diagnostics.
Patching is just delaying a bigger issue, a pinhole at the top means the metal is already thin from the inside. Bleeding it first to see how much water comes out is a fair test, but at 15 years old I would just change the rad and put new valves on. Cheaper than mopping up when it lets go properly.