Roger,
RE: extended warranties, I don't know about the specific company you're referring to but in general extended warranties are a very good idea on late-model MBs due to the significant cost of electronic parts especially. I had a GE extended warranty on mine, up to 70,000 miles, and got more than my money's worth out of it.

RE: the navigation system, if you don't get any replies on this you might want to re-post with a more specific subject line.

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Steve
'93 400E