Save yourself some money and buy 5ltrs of Autosmart Brisk VIF Low foam upholstery cleaner. They also do a foam can spray.
Its concentrated so a little goes a long way.
It will shift the most stubborn stains from car seats , headlining, mats, carpets etc,etc.
First check if the seat has a "nap", if yes, be carefull as too much scrubbing can damage this!!!
Mix up a solution in a 500ml spray bottle,cover surrounding area with a large old sheet. Dont just spray the effected spot!!!, but cover the entire seat area.
Now with a soft gentle baby brush, gently agitate the seat cover, dont scrub too hard.
Now wipe away with a clean microfibre cloth.
If its a stubborn stain, get a bucket of warm water, and after scrubbing repeat the process using a microfibre cloth, keep rinsing out the cloth to remove the dirt.
Now leave to dry ( bang the car heaters on and make a pot of tea).
If its a really ground in stubborn stain, let the car seats dry after the first clean!!, then see how it turns out, best to leave the seat for a while before carrying out the next clean, be patient eh!