Ok ON my 92 300SD I got three issues same area.

1- Temp gauge is on 80C and then goes to 120C I tap on the glass and goes back down to 80C. Any body knows how to fix the temp gauge? I know the problem is at the dash board, beacuse I move the plate behind the gauge and the nedle moves up and down. Is there any replaceble parts on the gauge?. I do not want to replace the whole board beacause the miles will be different.

2- The temp sensor sending unit at the head block I check for Hms and was reading 56 to 57 Hms, according to the table the temp will be 86 to 87. Is any other way to do another test for accurate temp reading?.

3- Also is the fan clutch, after the car is shut off will take 2-3 seconds to stop. How to test the fan cluch?

Thank you guys in advance for your ideas and advices.