my girl's 300td sprang a coolant leak this morning. i have found the souce but do not know what to do about it. the leak is coming from the side of the block. from a circle "plug". it looks very similar to where the temp sensor is located but the hole has a plug or something in it. it is weeping pretty steadily. i have a pic on my phone and will try to post it soon .any help will be appreciated.

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"Canary Mercedes
Crawlin' like a baby
Drank got me lazy
Iced out, Feelin crazy"
- Riff Raff