I have had my SL out this summer about 6 times.
Each time I have had spirited drives, with rpms revviing over 4500+ around back country roads, and hills; and 70mph runs on the highway.
The first drive was on 1/4 tank from last season and was rough; i have been thru a few more tanks, and let the reserve llight come on and drive 15-20mi+.
I have learned that when I babied the SL and tooled around it would always run so-so, shift harsh, brake mushy, burble, gurgle, muffle back fires, and have strong exhaust fumes.
However, after I started really running her hard she just runs better. Esp, running thru a tank till full bottom , and not topping up stale fuel. I have had 17 gal fill-ups on my 250 SL 18 gal tank; where in past I was getting 10-12 gal fill-ups at best (keep nozzle at 1/3 pull and sideways)
The engine runs cooler, shifts are smoother, the exhaust is cleaner, sounds better, and the backfiring is gone. I am convinced hi RPMs runs really clean sludge from the internals from radiator, FI, to plugs, to exhaust and even transmission fluid.
Run em fast & enjoy a better SL