So my car has been starting to have the mold/mildew smell, and a friend told me that I would have to remove the leather cover to check for any. Any idea on how I can do that?

Jesus don't remove the leather! It's probably coming from your ac vents, or your footwell carpets if they have ever been wet.

Well my rear seats have been wet before a few months back when my friend had an incident and threw up in the back seat. I tried to clean it the best I could, but this the only thing I can think of that can be the result of this. My footwell carpets I highly doubt cause I have weathertech for that.

I’d still check the footwell areas even though you have the all weather floor mats. In some cases, a sunroof drain hose could be leaking into the interior or a crack could have formed in the windshield urethane causing water to leak behind the a pillars or firewall. The same could be true as well at the rear windshield areas for the same reasons. Body sealer can even give out as well allowing water to seeping into the cabin. I hope none of these are your case, but just throwing it out there.

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