OEM vs. aftermarket parts, which one should I go for?

No matter how well you have maintained and cared for your Nissan or Infiniti, eventually, you will have to buy replacement parts to replace the old and bad ones. The replacement parts can range from internal mechanical engine components or something minor like a fuel pump to a new radiator and headlight assembly.
Are you better off sticking with genuine Nissan parts, or getting an aftermarket replacement manufactured by a third party?
It Was Probably Aftermarket To Begin With…
Since the beginning of the Industrial Age, it has been rare for all components of any machine to be made “in-house.” Even Henry Ford would obtain generators, tires, springs, etc. for his Model T from outside suppliers.
It’s not cost effective to manufacture every part in one facility. In fact, ISO certification actually requires that each vehicle manufacturer have multiple sources for many parts so that if it becomes unavailable from one source, there is always another supplier from which it can be obtained. Therefore, your Nissan fuel pump may have been manufactured by any number of companies.
Packaging – and Property Rights
What often makes a part like this “OEM” is, believe it or not, the package. On the outside, it may be labeled as a “genuine Nissan part,” but if you open it up and look at it, you may find that it was actually a Bosch fuel pump. (Auto Parts made by different companies can also vary a great deal in terms of quality, which is why one vehicle of a specific make and model can be trouble-free for years, while another identical vehicle may be a complete lemon. It happens.)
When a new model is designed at the factory, the company assembling the vehicle will enter into an exclusive contract with these outside manufacturers to provide them the car parts they need, to the required specifications. During the first year or two, the company is obligated to provide these parts only to the original manufacturer and its dealers – in this case, Nissan. However, this exclusivity clause usually expires at the end of the second year – and these companies are free to distribute them to any auto parts retailer, or offer them directly to the public.
There are many small companies that specialize in manufacturing improved versions of a particular component of a type of vehicle. Sometimes these products are extremely specific to one particular make and model, such as Chevrolet Corvettes built between 1995 and 2008. Common examples are high performance exhaust components and intakes as well as brake shoes and rotors. These kind of aftermarket products can be expensive, but can also greatly improve your vehicle’s performance.
What About Auto Body Panels?
If your fender or hood is damaged beyond repair or your insurer determines that an aftermarket replacement will be a more cost-effective way to restore your vehicle, that is what you’ll get.
Some insurance industry tests indicate that aftermarket parts are just as durable as their OEM counterparts, observing no substantial difference in crash tests. Another source from the National Association of Independent Insurers points out that while the U.S. Department of Transportation regularly issues recalls for OEM parts, so such recalls have been issued for aftermarket parts.
On the other hand, many body and fender repair people say that aftermarket panels are often made from inferior materials, or fail to line up correctly when installation is attempted. Currently, there are several cases across the U.S. in which this issue is still being litigated.
There is an agency called the Certified Automotive Parts Association that tests aftermarket parts and certifies them if they are determined to be of the same quality as the original. Chances are that if a replacement part has been certified by CAPA, it will be equivalent to your damaged OEM panel. In any event, you have the right to know whether or not your vehicle is being repaired with OEM or aftermarket parts and negotiate with your insurer.
Shop Around
Of course, the biggest factor in the cost of replacement parts for your vehicle is determined largely by the number of middlemen involved. Whenever possible, try to get your part directly from the manufacturer, or from a retailer who deals directly with the company that made it.