Timing chain guides/rails - Exterior temperature gauges

I understand (e.g. from this site) that timing chains can last a long time on M103's. However, since I am not the original owner of my car (1991 W126 300SE), and to be on the safe side, I decided to have the
timing chain changed at its current 127,500 miles.
I had also understood that it was advisable to change some timing chain guides/rails (and maybe sprockets, etc.) in the process, so I was surprised when only the chain and tensioner were replaced. When I inquired I was told that changing guides/rails is both unneeded and a "big job" on the M103's, and that it's in fact only needed on the V8's (i.e. M116's & M117's).
Changing subjects, my exterior temperature gauge currently either is blank or displays temperatures in the 130's. I was told that the whole dashboard must come out to look into the problem.
Opinions on any of the two subjects above? __________________ 1991 W126 300SE
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Every timing chain I have ever done has come with new sprockets to match.
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I had always heard that guide rails are a big job and rarely break. As far as ext. temp sensor, maybe the sensor is bad? It's behing the license plate. Richard

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