I hope you guys can help me to fix this problem .i have a c320 05 sport
Found out I now have an antifreeze leak from the bottom
Seems to be dripping from the coolant drain plug, I retighten but didn’t work . I see a small hole above the drain plug ,( whats this ) ?? There comes out coolant but it looks like a air valve ???(is this normal ?) Any ideas ? Holes , everything it’s OK , all this happened after I did a coolant flush , thank you ...

 

If you're sure it's not the coolant drain plug, trace your way up.

Not sure about the C320, but the C230 has plastic coolant pipes that break around the 12 year mark. In each case, the pipe cracked where the O-ring was, as the thickness was reduced at that exact part of the pipe. Personally I had 3 of them fail this way, each time causing a slow coolant leak like the one in your photo. I fixed the problem once and for all by replacing every single plastic coolant pipe I knew of on the engine. Now I'm good for another 12 years or so. Of course I'm hoping they've improved the material since the time my car left the factory, as the part numbers were different.

See this thread to understand the troubleshooting and repair. As mentioned, the link is for the C230, but you'll have to go through a similar process.

Good luck.

 

I will do that ! Thank you 👍🏼👍🏼👍🏼👍🏼