Funny you should mention, as Rockauto came to the rescue for the transmission kit, and Advance for the spark plugs. Now I only go to Amazon if the car part isn't on Rockauto, but it begs the question - if this part is so obscure it's not on the specialty site, can I really trust this Amazon listing is actually the part I need, and that I will not instead receive, say, a used birdhouse?

I got my tranmission rebuild kit from RockAuto as well ;)

The auto parts world is a tricky beast. If it's not sold by a major retailer, there's often the manufacturer or specialty sites for various classes of autos, especially classic cars and 4x4s. Ebay is another great place for used parts as well.

I have Prime, but I buy auto parts on walmart.com. Free shipping to the store that I drive past every day, better prices, no commingled inventory.