1987 Porsche 911 — what changed after 100k miles?

Write down what you already tried. A second data point from another 1987 Porsche 911 owner helps more than a generic diagnosis. That's where I'd start. Post the numbers (or the code) and people can get more specific. Might be overthinking it, but I'd rather overthink than overspend.

Thanks — that narrowed it. I'm going to try the simpler check on the 1987 Porsche 911 first. I'm keeping receipts and dates in one folder.

Don't overfit one forum story to your car. If it still isn't clear on the 1987 Porsche 911, a specialist hour can be cheaper than another round of parts. I'd do that before spending real money. I'd want a dollar figure or a measured spec, not 'should be fine.' I'm keeping receipts and dates in one folder.