Found my dads original 1971 duster!

Hey guys. Gonna try replacing my temp sensor and see if that fixes my temp gauge issue. I topped up coolant this morning and ran car for 10 min and gauge still didn’t move. Is it a sensor I can get at an auto parts store, or is it specific to a 71 duster…and needed to be ordered from a place like classic industries?
The current sensor has teflon tape on it, but it worked for the first few drives. Should I try taking it out and removing the tape, or just wait until I get a new one?
Also, after a 10-20 minute drive, my ear cap makes a slight hissing noise when I check under the hood. Is that normal? Thanks guys. Here’s a pic of the rad cap

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