A litre of oil in 1600 kilometers (about a quart in a 1000 miles) is not terrible consumption. I wouldn't get to worked up about it. You could do the seals, and that would probably reduce it greatly.
Are the plugs fouling?
Our 1990 190E 2.6 uses a litre every 1500-2000 kilometers in heavy city driving in hot weather (uses less in cooler/highway conditions). The plugs aren't fouling, so I'll just leave it be. That engine has about 200,000 miles.
1998 C230 "Black Betty"