Suginami,
as a former high-school teacher I thankyou for correcting my grammar. but as you stated in your post : I am infact referring to neither all the mercedes automobiles nor the company mercedes. I'm merely referring to my own "single" car as a "single" owner.
At this point I'd rather not discuss this any further however your post provided a good laugh due to the fact that the 15 thousand hits that post has and with almost 350 replies, you're the only one who has totally lost touch of the original topic the post is intented to discuss and you're concerning yourself with the grammar of the whole issue.
every heard of "thinking outside the box" ?
good luck to you. and i hope you've progressed further than high school. as for your disclaimer.. are you suggesting that a native speaker of english with no former education would have more command over the grammar versus a non-native english with a phD in english literature ?. if so... i rest my case.