Curious, but what's the difference between an '80 and, say a '79?

I'd love to buy any SL for a second car. They're all so much money (for a good one), and I really don't have the space for it.

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2003 S500 Black/Charcoal
1990 560SEL 61k Arctic White/Grey

SOLD:
1988 420SEL Black/Palomino Sold @ 85k
1987 420SEL Midnight Blue/Grey
1986 420SEL Diamond Blue/Grey
1983 380SEL Champagne/Palomino