The bad news is all the rubber/plastics under the hood which perform a sealing or insulating function is approaching or past serviceable life. The better news is that many of these parts are relatively inexpensive, at least compared to sensors/mechanical components.

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1988 300E
1993 300SL
1994 540i

If I have a problem with my Mercedes, I go to MercedesShop. If I have a problem with my BMW, I go to BimmerNut.
If I have a probem with my Dell, I reboot it. I was an engineer for them for 10 years and we blamed everything on Microsoft.