Gas mileage on '81 380 SL

Bought it about 2 months ago, 116,000 miles, runs great, and mechanic says engine in factory spec shape after tune-up. BUUUUTT, I am only getting about 12MPG driving easily around suburbia. Is this normal and
am I expecting too much? BTW I am no hot rodding lead foot.
Chip
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According to fueleconomy.gov on 1985 380SL, you should get 14 city and 17 highway. With an older car, there are alot of things that may cause lower fuel mileage...leaky vacuum system... timing chain stretch... timing is off...fuel injection leaking internally that you are burning too much fuel... cat converter nearly plugged...
Your car takes regular and that all you should put in, you don't benefit with higher octane gas.
I had 84 380SE, I always had 17or 18MPG regardless of highwy or city.
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