Most likely, it's the aluminum and the steel from the clamps expanding at a different rate... Most likely nothing serious....warm the vehicle up in a garage for a day, and see if it still leaks. Then tighten you clamps a bit...
Don't tighten clamps on plastic while the plastic is still cold. The plastic in my experience can shatter...

__________________
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Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic