Our bodies emit some really acidic oils, was in the cosmetic industry for a few years.
Look at the pattern, you are a big guy, sweat contains not only acids, but other corossive elements, such as salt, proteins, etc.
There is no real answer for stopping this, as we never know today the actual quality of the leather used or the even application of the clear on leather.
The passenger seat is an example of this, it usually gets less seat time, but the leather may not be of the same quality as the drivers side.
The other issue is the amount of UV's which may strike that seat and degrade the coating.
Both Zanio and Mequiar's make good products, they don't use damaging oils in their forumulations, to my knowledge. Doubt very much that they would have any effect on the issue.
All I can offer is for all here, clean the seats of body oils regularly, using a mild, non-butyl cleaner and then wipe with a water dampened towel to remove any residue of the surfactants in the cleaner from the leather.
If you wish to "dress" them, use a water based PDMS, and there are many good products out there for you to choose from.
The damage to your seats is done and there are no miracle products to correct it. Of course, just like our ladies, we could apply some "make-up" but that won't cure the concern, only cover up the concern.
For those who would like to understand the "body oil" issue, go to a friends vehicle that is never cleaned on a regular basis and apply a water based cleaner to a white towel and just wipe and rub a bit where they rest their arm below the window on the drivers side, that is all.
Look at the towel, the "soil" is something else.
You don't really notice how much the oils have built up on the area, but just look at the towel.
Oil-crude, makes up most of the coatings, fabric etc used today in vehicles.
If you wish to return the substrate to it's natural state, just subject it the compound which created it, "oil". From your body or a product.
