I have a '91 300E M103 with 230K miles on it. I'm wondering whether to fix it up or find something with better gas mileage. I'm getting about 15 MPG driving stop and go around town, never more than 40 mph, barely cracking the throttle, revs under 3K. Mixed city/hwy is more like 20 MPG. I've never taken a road trip in it but from a few long drives on I-25 along the Front Range, it seems like I could get 25 - 28 MPG. How does this match up with everybody else's experience? What's the best possible MPG I could get?

Thanks for the help.