AM Radio reception fades in in and out

Thanks guys,
My microvoltaic head is now clearer. I do have the original, very long, telescopic antenna, although I don't keep it fully extended as to not hit the top of my garage door. I like the theory of a failing capacitor, but couldn't a tube react the same way? My radio is not solid state, and has 5 vacuum tubes. I think my next recourse is to test the tubes and proceed from there. The tubes, according to my shop manual, are:
12GA6
12BL6
12AE6A
2N573
MN-29 or 2N176
I'll try to keep ya posted...