[Water Warrior 2]

Neglected seat. First thing that pops in my mind is a bucket of water with a mild soap. Soft bristled brush of some sort and enjoy. The seat is vinyl so you won't hurt it. Also you are right about Armorall. Never ever put any finish on a seat that will make it slippery.
Got a good lesson with the stuff a few years back. A friend cleaned up his old pick-up. Then he applied Armorall to every surface in the cab including the door panels and rubber floor mats. Vinyl seats included. After 3 tries I was able to get into the cab without slipping and sliding about. After the truck started to move I felt like an insane piece of Flubber.