Mine was still bright and shiney. Like it had never been opened and the cap had been sealed up tight.

I wondered about how to tell if it was working also, until I heard the hissing sound after a minutes or so. I love the plug!

It only takes a couple of hours to heat up the engine, especially if it is in the garage. I have mine on a timer in the winter.

The other thing I do is loop the cord through the steering wheel. It is hard to forget to unplug it that way!

-Jim

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1995 S350D, Green with black leather interior.
Bought January 2008 w/ 233,xxx miles.
I did 22,000 miles during the first year of ownership.