Toyota Main Service Center (Qatar) review: Unknown coolant leak (decreasing of water level inside radiator tank)

After smooth and regular services/periodic inspections I'm doing it to my car, I have been requested by Toyota main service center (Qatar) to do an overhauling of my Land Cruiser engine (vx-r, V8, 2015) due to "Unknown leak of the Radiator tank. This issue was like a disaster and couldn't believe it since my car is well maintained and never ever had a major damage/issue before.

The case has started when I have noticed the coolant tank level was decreasing regularly and very fast, although the engine's temperature was never shows overheated or the engine's light turn on.

As non-expert person, I was expecting this issue due to weather condition, and could be one time case. Unfortunately, I was filling the water regularly, so I have decided to send the car to service center for more investigations.

I have been told by the service advisor to do some repair of all hoses & gaskets in order to do a pressure test, and then test drive.

After the test drive, they have noticed the water level is decreasing!

Thus, I have got a call by service advisor that the leak is still there, and the next step is to do an overhauling of the engine! So that they will be able to confirm the issue and get the right estimation/repair.

This is totally strange with respect to all routine services I'm doing to my car.

Plz note that I'm sending my car to the service center every 10,000 km - 15,000 km; so as a professional company, my expectation from the service center is to do the inspection and repair in proper manner, and to find out all discovery jobs (Unexpected issues & take a proactive action).

After overhauling, there was a huge damage to cylinder head, and a major repair should be done under my budget! Which is not acceptable at all due to several reasons:

1- I'm sending my car regularly to do a professional repair, and defiantly they should be able to find out earlier before it goes worse.

2- We have noticed that during last visit and job card, the service center has found out that there was a leak in the same area, but they could not recognize where exactly the leak coming from (Lack or technician experience and knowledge). So they changed the cap only.

The service customer care has informed me that is this due to equipment failure, and my car is not under warranty any more!

I have told them that it is not about warranty because it was their mistake as they did not find out the issue earlier during last visit due to manpower experience/knowledge.