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My sister just picked up a pre-owner GLA as her first car that bought with her own cash she saved up. It’s a 2015 and while I helped her check it out, I didn’t see this in the engine bay.
It's always difficult to diagnose from online photo's but does appear to be a chemical reaction. Clean the area thoroughly and treat any rust with a neutralizer. Then regularly watch for any moisture or other recurrence.
I've got a couple small areas where the factory was sloppy with seam sealant application, perhaps robotically missed and touched up by hand.
It could be that as well. I've had mice chew on the firewall insulation (nest material) on another outdoors vehicle in the dead of Winter with high snow and thereby diminished cat patrols. Mice love to chew cable insulation as well to grind down their teeth.
So mr inkredibul, is it loose material or something adhered to the metal?
Originally Posted by prktkljokr
It's rodent damage, looks like they have chewed the insulation.