[firstgenaddict]

Here is what I did to remove the stains from mine.
I tried many different cleaners on a build sheet that didn't matter and figured out what worked best.
I used a quick paint thinner from the paint shop.
It is what we use to clean paint guns.
What I did was to lay down a stack of about 5 paper towels and put the build sheet on top of it ...face down.
Then I poured some thinner into a jar and from the jar I liberally poured the thinner over the back of the build sheet(there was alot of thinner). Then I took another paper towel and bunched it up into a wad and blotted the back of the build sheet (do not rub... BLOT), the thinner released the tar stains and the paper towels on the bottom wicked the thinner from the build sheet. You may have to repeat the process multiple times. Always replace the paper towels when repeating the process.
Test it on a corner / not the whole thing.
I tested on a corner and it worked great, then I tried a little where the printing was and it did not destroy the printing so then I went for it.
The build sheet was so stained that you could not make out anything that was on it, now everything is legible. It has been done for over a year and there has been no fading of the print or anything else.
This works great for tar but will not take out ANY RUST STAINS, If your floor was rusty and stined the sheet I do not know what to use... I have tried everything one that has rust stains.