"...If you get it from a Volvo dealer it is OEM. If not it is aftermarket..."

Not quite so. There is at least one local independent near me that gets his parts directly from the the Volvo parts distribution warehouse in Atlanta - blue box, Volvo logo, etc. Even if they don't have it in stock, as long as I call him by about 10:00 or 11:00 in morning, the part is waiting for me when I get off work. I believe some of the other suppliers like FCP also offer Volvo blue box parts to people that are willing to pay extra for the quality and fit compared to the aftermarket stuff like Beck Arnley, etc. That's just one thing I like about Volvos. For example, I don't know that you could purchase authentic GM or Ford parts from an independent like that.

Now, as someone in this thread pointed out, it may not be 100% identical to the part your Volvo was built with 25 years ago, but it IS the same part you would get at the dealer's parts counter, which is about as good as you can do. Generally you just get it for a little less money through the indy.