Agreed, but since I just found this thread, I'm going to add my two cents anyways.
I've been a parts counter worker/parts manager for 7 different import brands. (All with the same company; yes I'm competent and can keep a job!
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The number one most important thing to remember is that your car is an import. These cars are sold in many different markets with different crash and emmisions standards. This plays a large roll in the design and function of parts catalogs.
All of the brands I work(ed) with often display part numbers for other markets even if you set defaults to North American market. So lets say your asking the parts guy (or gal) to look up a bumper for your '98 RS. He might get ten listings, but only two apply. Now he has to try to read though all the footnotes being careful not to misread and taking considerably more time. If he had the VIN in the first place, the catalog might have only shown the one or two choices. And most walk ups have more then one required part, and often lots of inquiries about prices of others.
I've read several posts in this thread about the inconvienience of having to get the VIN. Please. Churning butter and plowing a field with an ox is an inconvienience. Parts departments are generally a fast-paced work environment with little down time between phone calls, technicians (or mechanics if your like that term better), and walk ups. If your asked for a VIN, it's to save the dealer and well as you more time.
As already stated, VINs more accurately filter parts. Then there was a chorus of posts about incidents where VINs were provided and the wrong part was still obtained. Just like anything else in life, nothing is perfect. But please don't assume that because it was wrong, the VIN therefor shouldn't be necessary. It could have been something simple as a bad listing or filter in the catalog. Sure, you've been inconvienienced on this part, but the system is 99% accurate for the tens of thousands of other parts on your car.
Lastly and most importantly
PARTS DEPARTMENTS DO NOT RECORD YOUR VIN! The manufacturers do not ask us to record it for them, and once your leave we have no interest in your VIN number. It does us no good. Zero. Ziltch. Notta. So please, lets be mature and no more posts about kakamamie theories as to why the VIN is required. It's to make looking up parts easier. Period. If you've never worked in the business, you just plain don't know what your talking about.
What you don't want to do when asked for a VIN is be a d**k like some have suggested. Put yourself in the other person's shoes for a minute. They don't want to get you wrong parts, and they certainly don't enjoy getting them returned. You take a lot of fire working on the parts counter. Your nobody's hero when everything goes right, but your the devil reincarnated if someones vehicle is held up because of your mistake.
The reluctance to look up parts without the VIN comes from those of you who lack the patience, understanding, or just plain commen sense about what is involved here. Your car is a complex machine with lots of parts and mistakes can and will happen. So instead of being defensive, evasive, or just plain rude, why not try providing the information and build a relationship with your parts department. My dealer rewards great customers with discounts.
Anyways, sorry to be so long winded, but having spent considerable time on the other side of the "you don't need my VIN" crowd, it's a subject near and dear to my heart.