Thermostat too dirty

Hello. I removed the thermostat last fall during winterization, and now I wanted to install the new one, but the hole inside it look extremely dirty. Looks like grease and mud, not exactly sure. I didn't notice it previously, because it was full of water (or antifreeze) previously.
Attached are the pictures. Is there some method to clean it before I install the new thermostat? Or I just ignore it?
Thanks

clean the surface and reinstall not abnormal

Might be normal in very polluted waters.

Typical of any raw water cooling system used in fresh water. Knock off the big stuff and use it.

My 1976 evinrude is spotless in there.

cyclops222 said:

My 1976 evinrude is spotless in there.

Click to expand...

is it made of aluminum, probably. op is iron.

cyclops222 said:

My 1976 evinrude is spotless in there.

Click to expand...

Great, your parents must be proud. On a cast block what the op shows is totally normal

use a wire brush to remove the rust flakes, install new thermostat, sleeve, and gasket and go boating.

extremely common on a raw water cooled boat in either fresh or brackish water.

Allright, thanks folks. I cleaned it, and tried to re-install the thermostat back to its hole.
But a very strange problem, that beats me out. The white plastic sleeve protrudes out of the metal block, see picture 1 and 2. Aren't they supposed to be completely flat with the metal block?
Even I remove the thermostat picture 7, it still protrudes.
Picture 6 is with gasket on, and still not leveled.
Maybe I am remembering wrong? Should it be like in picture 4? In that case the gasket fits tightly.
Anyway, I ignored the protrusion, and installed it, but no good. The gasket is loose and water is leaking out.
The white sleeve sits on the thermostat nicely. How come it was flat leveled before?
The only solution I can think of cut of the sleeve off around 2 mm, or put 2-3 more gaskets.
Thanks