Try a product called "WET it and Forget it" I used it on my roof and the mold vanished in three weeks. Used it on my sisters siding and srayed it on and rinsed it the following day and it was clean. When I sprayed my roof I did not rinse it I let mother nature wash it off.

 

Simple Green....if you can get it. Amazing stuff for vinyl seat material. If mold and mildew is an issue, 50\50 bleach and water. I've used this on one of the boats we use that sits in water all summer and it works very well.

 

I think my issue may be unique with a tropical location.
I've had a couple of JD lawn tractors, and my new 1025r - all with the yellow seat.
Here in Hawaii we have an issue with constantly warm humid air - and mildew growing on leather, in closets, etc.
My vehicles are never left outside, but that yellow fabric on the seat always "grows" something on it.
It looks like dirt, but I don't think it is. Maybe a combination.
At any rate - it is difficult to impossible to get it clean and keep it clean.
I've tried a half dozen different products - even ones for mold.
But with all the little creases in the fabric, I just can't get it to look clean.
I soak it, scrub it, but it never comes close to how it looked when new.
Anybody have any suggestions, or at least tell me you have the same problem so I don't feel like such a maintenance failure?
What an impractical color for a tractor seat.

It is a dirt/moisture mix.

I'm in a unique subtropical climate and the same thing happens to the seats on my tractor and mower. I don't bother trying to keeping them clean on a regular basis, but when they get washed(about every 2 months), I use my electric powered pressure wash to clean it. It's a variable pressure washer that will max out at 1800-psi and works well for cleaning the seat. I use no detergent, just plain water ran through the pressure washer. It removes all the of the dirt/mildew from the seat grains and comes out looking almost new.
:bigthumb:

 

 

You could solve your problem by getting a Mahindra - then it'll be in the shop all the time and not getting dirty. :thumbup1gif:

 

Ouch.......