When I had the gearbox out, decided to replace crack pipe, thermostat housing and thermostat. I broke the coolant bottle return pipe (when changing mater cylinder) so only just today reinstalled a new bottle. After refilling about 2L of coolant, I noticed a alight leak - one picture even caught the drop in action! I guess I need to take the entire thermostat housing apart to locate the source? I've got lock carrier in service position. But still, access is pretty tight (compared to having the gear box out).