At first I was going to buy the 560SEL, but then the dealer has been taking his time with repairing/replacing the punctured tire. So, after considering that my 500SEL still needs waay too much work for me to be considering another piece of German metal, I've decided not to buy anything else until the 500SEL is in great shape.

Currently tackling the climate control / blower motor issue...

Thank you all for your help. I've definitely learned a lot on how to choose between two such cars next time!

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1999 Mercedes-Benz S600, 103K miles - garage queen
1988 Mercedes-Benz 560SEL, 89K miles - daily driver
2007 Hyundai Sonata Limited, 31K - daily driver