Ok, Garmin sent me a new antenna today. The XM works! Not sure what happened to my old one. The wiring and antenna seemed fine other than some cosmetic (?) scratches, and that's if these could even be classified as scratches.

I did notice that the XM reception bars were usually one less than completely full for a month or so before the XM completely went out. So if anyone is noticing less than full XM reception on a recurring basis, have Garmin check it out.

Upside;I got a new antenna for just the cost of me shipping out the old one.
Downside; Being without XM for a little over a week, and Sirius charging me a 15 dollar antenna change fee.