At this point I think you need to repaste your heat sink, you might want to replace it as well as it may have popped a leak to the coolant leaked out so its not transferring the heat effectively [https://www.thebookyard.com/product.php?cPath=96_257&products_id=8576|MacMini Server Heat Sink and Screws (2010)]
Follow this guide to get the board out [guide|3115] and getting the heat sink off.
* [product|IF179-010]
* [product|IF179-023]