I have not done what you are suggesting, but it sounds complicated/expensive, and I do have an alternate suggestion.

While my antenna was removed for repair, I temporarily rigged up a simple/cheap split wire antenna, the kind used for home stereo receivers that are mounted in cabinets.

Since it was temporary, I just layed it across the rear shelf. To my surprise, FM reception was just as good when straining to pull in the distant station I listen to on the way to work. There is one stretch where the signal gets weak, and it was no worse with the wire antenna. One of these could easily be mounted nearly invisibly by running the wires along the edges of the rear window.

I only reinstalled the power antenna because I had already invested in rebuilding it. If it fails again, I will simply toss it.

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1986 300E 5-Speed 240k mi.