W203 220CDI 2006 - Leaking Injector Seal?

I have been getting a smell of burnt diesel into the cabin over the last few days, had a look under the bonnet and find this:

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You can see the dark patch near the injector (the smudge is where I rubbed it with my finger).

Is it safe to say this is most likely a leaky injector seal?

Going to see this morning if its covered by my used car warranty (doubt it, nothing else has been), if not any ideas on cost to sort?

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