On my RHD W126 the drivers side of the hood has some play at the front while closed. When travelling about 50mph the right side of the hood will lift about 5mm at the front of the bonnet. I first thought that I hadn't shut the bonnet and it was going to lift up but upon checking there is play on the right side that is not apparent on the left side. I have checked but cannot see any way of adjusting this out. Anyone know?

I thought I noticed the same too on the 126. Open the bonnet and shut it with both hands on each side of the grill. Do it hard. Worked for mine. Otherwise, just check if the rubber lining has come way off. I have 2 rubber linings on each side - presumably to secure the bonnet?