Lowered fluid level in header tank and ran motor for perhaps 30 minutes without any change in level. Leave it alone and monitor level, it’s not going to stop the engine. I do have a theory. The engine was operating during high angles of heel, rotating the engine exhaust deeper under water, thus significantly increasing back pressure on the secondary water as it exits into the exhaust bend. Could be distorting a seal?
Water injection elbow was being a pain, old flat gasket. It kept on leaking so rather than risk breaking the m10 bolts it was Hylomar blue to the rescue again.