I bought this one from Amazon. I left everything from the ball down in place so as not to disturb the caulk. I believe I reused the screw also, the two halves just mate together. https://www.amazon.com/Magadyne-Recr...2788038&sr=8-6
The hardest part was deciding how to approach the roof without danger of denting the front cap.
Why yes it is. With AM/FM antennas they are not overly sensitive to the minor differences in impedance you might find. so if it looks the same and measures the same, you are generally in good shape.
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