No access from inside the passenger compartment. There's a removeable panel and gasket inside the front wheel-well to get to the antenna. The bolts/screws are probably covered in undercoat,dirt and rust. You should also find some sealer between the panel and the inner fender. It would be a good idea to clean out the fender cavity once you get the panel off and maybe treat/repair any rust you find.

There may be a number of small supplemental fuse boxes under the hood for radio, AC, power windows etc.... The antenna fuse is probably in one of them.

It's possible the contact inside the antenna is weak/dirty/corroded, though I've only seen that happen on a retractable Bosch antenna. You could connect a cheap aftermarket antenna to test the radio, before installing a replacement antenna in the car.

Happy Motoring, Mark

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DrDKW