My 1978 Avanti II (RQB2679 - just purchased this summer) has a Panasonic radio that looks like it might have been a replacement. My reception varies from excellent to non-existent with a great deal of fading in and out. I understand the antenna is embedded somewhere in the rear window trim - could that be the problem? I have suspitions about the whole radio unit because the cassette player no longer works, so the unit may be at the end of its life. I did remove the grill on top of the instru