Have you tried power washing it? It might not completely eliminate the stain but the whole driveway would probably look a lot better and it might satisfy the homeowner. There's always somebody around doing cheap power washing or you can rent one.

Thanks - we are trying an acid wash and power wash combo tomorrow - here's the before video -

Here is a link that might be useful: Before AcidWash+PowerWash

Looking at that video I'm thinking you will see a big difference. Even if it is not completely gone your landlord should be pretty happy with the effort. Good Luck. -KH

Here's a follow up video now - with Before/After split screen. There is a huge difference.

So far we have only done spot acid treatment of the stains, and power wash to it, but it is significantly better overall.

It's so much better than it was, we're hoping this will pass without any issues. I think if we had to go to court, a judge would rule that we improved the appearance more than enough to compensate for any perceived "damage". We will try to get him to sign off on it before trying anything else.

Here is a link that might be useful: Before/After Powerwash Video

the suspense is killing me...what is the verdict/outcome?

This shows the result after a powerwash and spot treatments using "The Works" at full strength for short periods of time applied direct to the stain. It's mostly gone, but still some marks show. Since it was originally DARK orange/brown stains, this is hopefully enough to be acceptable - the overall appearance of the driveway is significantly better than it was - so if anything we have improved the condition.

Here is a link that might be useful: Before/After video split screen