I bought a vintage 1965 Mustang bench seat for my 1968 F100 project. Seat had been sitting for 20 years or so in a guys attic.
I had heard about using hand cleaner and a brush so I gave it a shot.
It is as simple as it sounds. Put the Gojo on by hand and work in with the brush. Putting it on with the brush wastes more so just use your hand.
Here is a shot of what looks like tar build up on the top of the seat.
After you scrub it down, rinse it with a rag and some water. You can use a garden hose if the seat isnt ripped up.
After rinsing it off, I used Lexol Leather Conditioner
Seat looks almost as good as new.
Some things to note. The vinyl on this seat was pretty old and brittle in some places. In most cases as soon as I put the Gojo on it somewhat seamed to soften. If the material had already hardened it didnt seam to soften it much.