The usual warranty on MB parts is 1 year unlimited mileage.
I don't know of a good way to service that pump bearing, it's packed in grease and doubtful anything would help, so kind of on your own, try what you like.
I'd still bet that it's the fan bearing or maybe the idler you mentioned.
You can get one of those mechanics stethoscopes like Mike used (Mpolli) or use a long skinny screwdriver as a cheap alternative to a stethoscope, that's what I use (hold screwdriver handle up to ear and the tip of the screwdriver as a probe.
Gilly
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