I ain't no little Subaru trooper. I'm an engineer in the auto industry, I know how things work. Look, parts sold to an OEM/OES (OES is dealer parts) are made with MUCH higher quality controls than parts sold to aftermarket. It's really expensive to perform the level of quality control required for OEM, so aftermarket companies don't always do it. This is true even for parts that are made by the same company.
Example, widget A has a very specific length requirement. 100% parts sent to OEM are checked for length, and the bad ones rejected before they are sent to the OEM. Aftermarket they don't check 100% if it's too expensive. They might check 10%.
In addition to that, there are teams of personnel at the OEM to check parts before they are shipped to the dealer.
Make your own decision, aftermarket parts are not bad, but you have a higher chance of getting a quality, trouble free, part by going to the dealer.