Return Pipe Leak. Anyone experience this?
 

My question: has anyone else experienced this temperature-dependent leak of this pressure-fitted return pipe (item #3 in diagram)?

I recently (summer 2016) replaced coolant components (valley pan, H2O pump, thermostat, return pipe (#3 in diagram) and did preemptive repair of coolant supply line pipe (#1 in diagram). The initial motivation of this entire effort was to repair a leaking valley pan.

As the colder months arrived, I have a slow temperature dependent leak at the return pipe #3. When hot and pipe expanded, no leak. As the engine cools overnight, contraction apparently causes a small, very slow pinhole leak. I slowed the leak temporarily with silicone, and plan to replace the component very soon but not urgently this weekend.

If there are other threads on this matter, I could not find them outside of heater return pipe leaks, which are in a different location.