Latitude E4200 CPU overheating

Dear Support,

My Latitude E4200 laptop has been working fine for years, but I faced an CPU overheating problem last week.

Without any loads, it heated up to 60C. But with a medium load (60% - 70%) it heated up to 95C-100C and fan speed was ~6600 rpm but it did not help to decrease the temperature. After several minutes of such kind of load, CPU reached more than 100C and became throttling...

I disassemled my laptop to check if there some dust could be inside and cleaned it. No results, there was the same overheating. Then I looked under the heatsink and saw that the original thermal grease was completely dry...

I decided to replace bad thermal grease by a portion of a new grease meaning that dry grease could be the main root of the issue. But after replacing thermal grease and assembling the laptop I got the same high CPU temperatures again and the same overheating and throttling.

What the reason could be for this sudden CPU overheating? Could the heatsink's copper pipe be damaged? Should I probably try to replace the whole heatsink part by another one?

Otherwise I have no ideas how to solve this problem.

I would appreciate you for any help and/or suggestions.