I have the same car and had the same problem because I hate the stock halogen bulbs especially with the LED DRLs.

I recommend this: LASFIT H7 72W 7600LM 6000K LED Headlight Conversion Kits- Cool White Upgraded Philips Flip Chips-Hi/Lo Beam for Mercedes-Benz https://www.amazon.com/dp/B074M5SLBX?ref=yo_pop_ma_swf

They have the retainer built into the bulbs so that will solve that problem and they fit great in the low beam housing. For the high beam housing, I cut the rubber cap down the center a little for the cord to come through and then used electrical tape to prevent water coming in.