So this ebay link I actually can’t get to because i’m at work. However what it SHOULD show is an Australian made aftermarket fan clutch for a RB20DET.
A while back I got into an accident with my Skyline, I had it rebuilt. The clutch was wrecked in it, bent in half. I had to replace it. I wanted a new clutch, not some used one of questionable quality. OEM was >$600 and had a delivery time of two months. If I had known at the time how long the car would have taken to fix I would have got it.
The Dayco one I bought was the price you see (iirc ~$200). A normal price for an item like this on any other car. It also is said to be a quality item, but it has one MAJOR flaw. The clutch on it is so strong that it basically is on 99% of the time. You ever hear a garbage truck drive by you and you hear that fan that is louder than the engine? That is what this makes my car sound like lol. At higher RPM >4500 the engine finally begins to drown it out.
I am going to tolerate this however it is an important lesson. Unless the aftermarket part is a PROVEN upgrade OEM is the way to go.
Another exaple is suspension links and control arms. While the OEM ones may not be the best they are strong. The aftmarket adjustable parts for this car are known to be rather weak more often than not. Popular parts like those from Drifworks simply are not as strong and you can tell by looking at them. Nismo makes parts that are actually overbuilt and though near double the price are well worth it.