Refrigerator has odd smell

Our 9 year old Norcold refrigerator has what my wife describes as a "dusty" smell. It is functioning ok and has had the recall mods done. The temp is getting into the mid 40's by late afternoon, but back in mid 30's by morning. We are camped in the desert with temps around 90 and fridge on sinny side, so mid 40's might be the best we can do.

The odor is also in the freezer. It is NOT ammonia.

We've only had the rig 6 months and just noticed the smell about a month ago.

Any ideas? Thanks.