Bricks, Masonry, Asphalt and Concrete - Cleaning badly stained concrete

I have a customer that needs to have the concrete area by his front door cleaned. Over the coarse of 25 years, he has spilled oil based stains on it, paint, wood sealer, blacktop sealer, and who know what else.

I tried some cement cleaner (biodegradable) that I bought at one of the big box stores, and brushed it in, then took my pressure washer to it. It cleaned the exposed concrete well, but the stains remain.

Can somebody suggest a product that may work better on the stains? Or is it trashed beyond repair? I thought of an acid wash, but really didn't want to resort to that. There area a lot of bushes around the concrete.

Any info is greatly appreciated!

Id like to know an answer to this one also. I have oil stains I cannot budge with a pressure washer and concrete cleaner. Just like above the exposed concrete turns a nice white which makes the oil stain stick out even worse!

Ok,

So, by doing a little research on the web, I found out that TSP (trisodium phosphate), can be used to clean concrete and not actually etch it like muriatic acid does.

But - will it clean most of the stains I mentioned in my previous post?

Anybody have experience with the stuff?