I wonder when it fails if coolant enters the oil
The oil pressure would be higher than the pressure in the radiator with the engine running, resulting in oil in the radiator until it's shut down. Then it might be possible for coolant to get into the crankcase if the leak was big enough. The first symptom of a leak will probably be oily coolant. I don't see a problem with swritching to 1/4" tubing, until the tube tries to connect to the rocker shaft connector piece- - - - -that thread is for 3/16" tube.
Jerry
