have a look at this thread
95 e300d, moulding below windshield that windshield&wiper rubber seal snaps into?
One of our members here found it on jcwhitney - its the whole trim piece that attaches to the glass and allows that large lower molding to attach. This is the part Im mentioning to clean out with and use soap in its groove so the gasket can fit.
If yours is now missing entirely or is in poor shape. This would be needed.