Maybe try Barkeepers Friend.  

Eddie

Looks like it worked like a charm on the stained Le Creuset Dutch Oven they cleaned.  They used a solution of LCB and water as recommended by Le Creuset.

https://pudgefactor.com/how-to-remove-stains-from-le-creuset-dutch-oven/

Eddie

And I love LeCreuset so this is a common occurrence.  Here is what I do and it works every time.  Pour peroxide in the pan to the top of the stain and bring it to a simmer.  Dump baking powder in and it will foam up.  Let it simmer for about 20 minutes until the stain is gone.  Has never failed and I've had a few bad ones.  I keep telling him on this cookware you don't need to go above Medium(dish) but he still cranks up the stove.  I have started buying the peroxide and Baking Soda in large quantities at Sam's because I was using it so much.

I was in the LC outlet a few weeks back and she told me to buy some Easy Off with the yellow top.  She said it will bring the pan back to life.  I used it on a few of my older ones and the grill pan that had a lot of burned on grease on the outside.  I was shocked how well and how quickly this worked.  I haven't tried it yet on the inside because I haven't had a bad one since I got the tip.  I bet that would work too.

I would put it through the SC cycle of your SCO.

My first partner Michael used to run a flea market and I hooked up an early 70s FD Electra-Clean oven outside under the screened porch. He was running that oven a few times a week filled with LeCreuset, cast-iron skillets and pots, guardian aluminum cast iron and cast aluminum. 

All the other people at the FM were always amazed how clean his stuff was.

John L.

If oven cleaner works, so would granulated lye, such as for cleaning drains. Original Easy Off is basically just lye.

Wear gloves!

I really wish I would have taken before and after pictures of these two pans but I wasn't planning to post.  The rectangle pan with the metal handles was one I picked up at an estate sale for $5.  It was literally black.  Sides, bottom and handles.  They were actually sticky.  I can't imagine how someone cooked in this pan.  I bought it because I knew how well it would clean up.

The other is a stovetop grill we use fairly often.  It had spots where it was black and nothing would clean it.  I did one pass on the grill and it came out looking like new.  The pan with handles took three or four times.  I don't remember but the oven cleaner works so well.

I am in the process of cleaning all my pans now with the Oven Cleaner.  Oddly, the yellow cap version isn't available at our Kroger so I've had to buy it on Amazon.