water valve leak ?

[Takimo]

so i have this issue when i use my heater = coolant leak
and also no matter what temp i put it always feel like 50 degrees


so today i decide to replace my water control valve even if all the garage that i went this past 6 year didnt diagnose a failure in the water valve even if i ask them if it could be the culprit they say no.


so base on that picture, is there any visual sign that it could be a leak in the water valve ?