Just finished fixing today…in the rain haha so it was indeed the sharkfin. It was corroded as all heck inside there, and of course the seal was pretty much disintegrated around the perimeter. I replaced it with an aftermarket fin for now and it’s no longer leaking. but I sure did look silly all week to the neighbors since I had a salad bowl and towel on top of my roof this whole time. and now that I have the oem one off there, I now know the part # for it
mine is an 05 too. I’m assuming it has to do with the audio options, onstar, sat radio options. I have no idea what my truck came with since there was no radio at all when I purchased it. But I assume it once had both onstar and sat radio since there’s an onstar button and it had the shark fin ♂️
So what type of receiver did you buy? I've been looking at a Pioneer double din bezel. Did you change out the speakers as well?