Katie...it's about time for me to take the master bath shower doors off for a good cleaning, too. I've been less than happy with what I've bought over the years, even though I clean them pretty regularly, too. Care to share what product you bought at Sam's that you're so happy with? I just bought a bottle of commercial Zep "All Around" at Home Depot, but haven't tried it yet.
I've been getting something called ProForce Bathroom and Tile Cleaner at my local Sam's Club. However, I just noticed that it seems to be available only online now. Doesn't matter to me. I would crawl over broken glass to get the stuff.
I also forgot to mention that I use it to remove all tea and coffee stains from my tea pitchers/pots and coffee servers. I just spray a little in each container and, within seconds, I can rinse out even the toughest stains. My tea pitchers look just like new now.