Quality of aftermarket parts

[bobs]

Hi I have a question for you long time mechanics & shop owners. What is your experience with installing aftermarket vs OEM parts? Is the quality as good (or good enough)? Case in point: I'm looking at a fan clutch for my '97 S420. The OEM Sachs clutch is $500, one I found on eBay is $250, and another one I found is $80. I'm a firm believer in "You get what you pay for," so I can't believe they are comparable in quality. So what is your experience?

I bought one of those $14 replacement antenna masts off eBay and the thing turned out to be complete crap. It fell apart the first time I used it and I'm currently going through the RMA process with the seller, so I'm hesitant to go with another aftermarket part, but the prospect of being able to save $250 over the price of the OEM part is a pretty strong incentive for me.