You could have another problem with your vehicle causing premature failure of this part. Too many people jump to the "faulty part" claim without knowing the exact problem in the first place. The manufacturer wants to see the part and find out why the failure was caused. If its there fault and the part is faulty they have no problem correcting the issue. The problem is, most people are impatient and cant have a vehicle down for them to determine the cause, so they want a new part immediately to get them back on the road. This is where buying a new part comes into play. If your vehicle is the problem and not the part, the manufacturer or retailer shouldn't be out money. We just assume they have more money then we do so its ok if they are out.
How many people would pay for the second part they already have on the vehicle after the manufacturer finds out their product is fine and your the minority with a different problem? No way for them to get that back. They can always refund or send a replacement, but cant collect on something that is already sent.
We humans hate to get the whole story or take responsibility when we are wrong. Not saying that is the case here, but the manufacturer may be able shed more light on the situation. I have been in the aftermarket/performance parts industry for more than a decade now and have seen every angle of this scenario. There are very few manufacturers that wont back there products 100% often times outside of the warranty window. People also need to know there is a difference in manufacturer responsibility and retailer responsibility. Retailers are not responsible for faulty parts or quality control, this all up to the company that produces the item. A good retailer will make sure that the return and warranty process is handled smoothly. Often times, depending on the scenario I (retailer) will send out a replacement and pick up the faulty part for a customer, because I know the manufacturer will warranty the part just based on the shear amount that we spend with them every year. We get reimbursed the customer is taken care of and doesn't have to wait on the warranty process. Just be polite and understanding, dont start pointing the finger, it will get you farther in the end.