How would I go about fixing this? It's just grime buildup from over the years. I'm not sure what the fabric is, but perhaps someone on here can tell me by looking at it? What method, tools, and products will I need to use?
Theres a ton of solutions but start with something simple like folex, you can find that at home depot.
You can use a carpet/upholstery cleaner if you already have one on hand. CG Grime Reaper 5:1 would work great on this as well.
folex straight, or some kind of APC 10:1 with a brush to agitate would be what i would do. zep citrus 10:1 would probably be good as well.
Duragloss foaming interior cleaner and lots of white terry towels. Folex is also a good idea. Krud Kutter would work too. The white terry's are important, they will absorb the stain.
I have to put another vote in for Folex undiluted. You will need to reapply and agitate a couple of times since that stain looks quite embedded into the fabric.
Simple Green at 1:10 also horse hairs brush to agitate the fabric and some towels to soak up and remove the grime. Tuff stuff also works good just let it sit for a bit then agitate the area and soak it up, you will have to go over it a couple of times before you can get it out.
I would recommend that you first identify the material and then select a suitable cleaner. What is the vehicle make? Could this be Alacantra?
I'm guessing a Ford with cloth interior. But that's just my guess. I suppose it could be an old lexus/toyota too.