Seems like after age your engine producing black smoke which is causing this black spot on body above the exhaust tip. Go for Bilstein engine cleaner that can renew the engine internal component like new one and will help stop black smoke, pinking and missing (if any)
Check with Emarat, Enoc and Eppco as i remember seing this sometime back, cant remember where.
See if washer is still working or not?
If not then see the water jet, hose, or electric connection is loose???????
If it works, then probably you need to get that fault cleared up with computer diagnostic system.
Take a needle and slowly pass it in the hole from where the water is sprinkled out it will remove any blockage that the hose may have and see if you still face the same problem.
I dont think heat has any co relation, as anyways heat inside the engine is lot higher than africa, uae or antartica......!
Older engine logic i can accept it. Its better to change slightly early in hi run motors.