The brief
The E200's headlamps had gone yellow and hazy, the lenses cloudy and dimming the beam. He asked about restoring them, and the honest answer is that a headlight restoration kit doesn't really work in the long term. The lens has a protective coating, and once that breaks down the plastic underneath yellows and clouds and scatters the light, so the beam goes dim and patchy, a real safety issue at night. A restoration polishes off the old coating and the surface discolouration, but the new coating fades again before long, and it does nothing about any underlying problem like moisture inside the housing. The lasting fix is to replace the headlamps with new units that have their coating and seals intact, then aim them properly.
The diagnosis
A check confirmed it, both headlamp lenses were yellowed and crazed with the coating broken down, the beam noticeably dim. A surface restoration wouldn't have lasted or addressed it properly, so the sensible fix was new units. That's a headlamp replacement, complete new units, fitted, connected, and aimed correctly so the beam pattern's right.
The work
The old yellowed headlamps were removed, and new genuine Mercedes-spec headlamp units fitted, connected up, the bulbs and adjusters fitted as the units required, every fixing torqued to spec. The new headlamps were then aimed on the beam setter so the pattern and the cut-off are correct, and the lighting checked all round. A check confirmed a clear, bright beam with a clean pattern, no haze, and the lighting working as it should.
The outcome
Clear, bright headlamps with a proper beam pattern, no yellowing, and the lighting aimed correctly. The E200 went home with the headlamps sorted for good. A polish would have looked better for a while and then faded again, so replacing the units fixed the dim beam and the cosmetics in one lasting job, the right call for a part you rely on at night.