Sirius/XM antenna No Signal

For several months on my 2015 Murano SL, the Sirius/XM band would load very slow, usually right after starting the car. Then after a few days when the outside temperature was far below freezing, the SXM band would not load at all. Now SXM loads, but begins with the message "No Signal", then after 5 or 10 minutes it sometimes begins to play, but the signal cuts in & out. I lowered the back of the headliner, disconnected the green antenna connector, looked at the inside of the connector, which appeared clean with no corrosion. When I disconnected the lead, the radio display immediately showed "Check Antenna". When I reconnected the lead, that message went away, so the antenna connection may be good all the way to the radio head unit. The next step seems to be to remove all trim panels to get to the back of the radio head to check there, however I'm thinking the SXM circuit in the head unit may bad in some way. If so, I may check with a local aftermarket audio store for a possible replacement with current GPS maps etc. Has anyone here had success with an aftermarket head, and if so, what brand? TIA

Update 1/7/2024: My Sirius/XM reception gradually worsened to the point where it came in only 10% or less of the time. I decided to search for a replacement antenna, found a used one on ebay at an auto salvage yard. Ordered it, replaced it yesterday, and the signal immediately came through perfect. It's not a real tough job to replace, but helps to have long arms. Took me about 15-20 minutes total: release the upper section of the rear hatch rubber seal and pop the back of the headliner down, release the green connector lead & remove the large sinch-nut at the bottom of the antenna, push the old antenna up and out of the roof & stick the replacement down into the roof, then replace & tighten the sinch-nut and pop the headliner back up and replace the hatch seal. See pictures attached of the old antenna. I doubt there is a way to "test" the antenna to see why it doesn't work right, but someday I may remove the bottom rubber gasket and see what it looks like inside. I was fortunate to find a used antenna the exact same color as my car, so no painting was needed. BTW, I wasn't bashful about "make an offer" in the ebay listing. My offer was accepted immediately, probably because it was a "used" item.

I'm going to try this now. I'm having the same problem all of asudden