When installing the new CHT in my 75 2.0, I found out that the threads in the block are pretty much gone. I can get it to tighten somewhat snug without the washer, but Brad Anders says on his d-jet site that the washer is needed to transfer the heat to the sensor. Plus I am afraid it may vibrate out.

Looking for suggestions on a fix. Never done Helicoil or what's the other timecert?

Helicoil would probably be your best bet (not familiar with the "timecert"). Heat transfer from the head to the sensor is critical so what ever method you decide on shouldn't effect heat transfer.

Maybe a thin walled threaded bushing?