I'd like to share a recent observation with my 1984 300SD. I have 205/65R15 Toyo Proxes H4's. I haven't been very diligent about checking tire pressures, and I noticed that my left front was a few pounds low, and the rest of my tires were about a pound low. I increased the pressures to 29 psi front / 31 psi rear.
MB recommends 28/30 but the gas station with the free air pump is about a mile drive and it was a slightly warm day, so the extra psi should not be an issue when it cools down.
Anyway, prior to doing this my car seemed a bit "squirrely", almost unstable under certain conditions. Balancing the tire pressures so that both tires on each axle were within a quarter psi of each other seemed to help much more than I would have expected. I noticed improved "tossability" and crisper turn-in. Stability at 70 mph was improved also. Just my observations...