Rubber Cargo Tray Emits Oily Substance

Here's the layout of the cargo area in my wife's 2016.5 CX-5. Because we had a 120 lb Lab mix when we bought the car, we opted for the soft cargo liner that covers the rear of the back seats, the rubber cargo tray and the rear bumper guard. You're probably thinking why all this protection. Well, our dog(RIP) was huge and my wife is hard on vehicles.

Now on to the situation at hand. The first time I thought my wife might have spilled something on the rubber cargo tray. I took it out to clean and noticed the same oily substance on the underside (wth?) So, now fast forward several months and the oily substance is back and in the same location. I remove the cargo tray and checked the cargo liner - no oily substance. I lift the cargo liner and checked the carpet - no oily substance. Has anyone else experienced this?

I have the OEM rubber cargo tray over the OEM carpeted cargo mat, and never have experienced oily spots. What's odd is that at first I was going to say that I didn't think it was something like a chemical reaction occurring between the layers of materials given that it is more spotty than not, but then I noticed that the two spots you show on the top view appear to be identically located/shaped in the under photo--if that's true, that does suggest it may be some type of reaction or leaching. I recall some owners having issues with greenish-discolored OEM all weather interior mats, but nothing like this previously that I've seen on here. To the finger, does it feel truly oily like oil, or more like something silicone-based? Or are they more like shiny spots that don't feel that different to the finger?

I have to agree about the leaching or chemical reaction. To the touch it feels and looks kind of like a cooking oil. It actually builds up a pretty good amount on the bottom side. I've taken the rubber mat out and may do the same with the soft cargo liner. They were both new, right out of the box when they were put in the vehicle. Maybe some fresh air will allow some of the trapped chemicals to escape and hopefully put an end to the "oily substance mystery."

RL, thanks for your reply and input.

You are welcome! When you use it, does the soft cargo liner run under or over those spots on the rubber cargo insert? If so, maybe there's a chemical reaction between the two materials, or from something on the surface of the soft liner. Still very odd that there are spots versus a more general surface issue if it is a chemical interaction causing some type of leaching....unless there's something on whatever touches or sits on the insert at times but not always. I know you already checked the actual cargo liner.

PS: I did confirm online that dog urine should not damage rubber, assuming that the insert is made of actual rubber or something rubber-based, but to have urine still around after you lost your dog (sad1) would also be unlikely.

Yes, the soft cargo liner is under the rubber cargo tray. I've had the rubber cargo tray out for several days now and the spots have not changed at all. I even had it laying out in direct sunshine this morning while piddling around in my garage. Since we lost our dog in May, I'm going to leave the rubber tray out to let it breathe, or until the wife wants to go visit her Mom.

Thanks again for your thoughts and input.