Your issues remind me of a similar problem I had early in my career with feedback wire resistors in control valves. Same extreme conditions and quite valuable production loss of it fails. Eventually the feedback sensor was changed to a LVDT electronic sensor with magnetic position. It does cost more but you never have to touch it.

Rusty. WA8ZID

From: "Joseph B. Fitzgerald" jfitzgerald@alum.wpi.edu To: "amsat-bb@amsat.org" amsat-bb@amsat.org, Rafael Pena pinoleronica@hotmail.com Subject: Re: [amsat-bb] G-5500 AZ Potentiometer Message-ID: BLAPR22MB21154EF2DF94D500F9FD719187AB0@BLAPR22MB2115.namprd22.prod.outlook.com

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I didn't find a supplier, but I did find a datasheet. You can probably find a replacement from a different manufacturer.

Curiously it is only rated to -10C.

https://www.tocos-j.co.jp/tocos-j-wp/wp-content/uploads/2019/06/RA25_Series....