Best way to clean line x bedliner?

With the exception of maybe 3 days I've had a topper on the bed since it was line x'd about 8 years ago.

So it hasn't faded much, but what's a little asthetically unpleasing is the fact that it's picked up some staining.



So far researching this I've heard:

Dawn dish soap (blue) + warm water + stiff brush

Simple green + stiff brush

Purple Power + stiff brush

powerwash

black spray paint (lol)


I was wondering if anyone has any recommendations/experience

Thanks in advance
MM

 

I hear simple green or purple power with a brush works well... Some say you can squirt some tire shine or tire foam on it and it will absorb over a few days making it look newer again.