Cleaning Drip Pans, Is it Possible?

Having worked in the apartment rental industry for 4 years now, one of the most commonly charged damages is drip pans.  Having also rented myself, the cheap drip pans that are provided with the stoves are impossible to clean.  I could not believe what a waste it was to have to replace the drip pans and be charged $40 for new ones (although I could appreciate that the drip pans were clean when I moved in).  I was able to keep the drip pans clean for the first 6 months I lived in my apartment by literally scrubbing them after they cooled every time I cooked, but then life happened and I wasn't able to keep them as clean over time.  I would love to be able to find the magic touch that would keep my residents from being charged when they move out and would keep my kitchen looking cleaner.

I followed several blogs from Pinterest and googled a few as well, and have had varying levels of success.  Here is what I've tried so far:

Boiling water with baking soda.

Before Treatment

 

After Treatment

Cream of Tartar w/Vinegar Paste Overnight:

Before

After 30 minutes it looked like it was doing something as indicated by the brown color in the paste.  When I rinsed/scrubbed, it looked quite a bit better.  I re-applied and left it overnight as the instructions indicated and there was no further change. 

 Tarn-X
 
Didn't work, not even a little. 

Heavy Duty Oven Cleaner:

Before:

 

After:

After all of the attempts, this one seemed to work the best, I left it on overnight and scrubbed in the morning.  Unfortunately, this was the cleanest I could get it which would would still earn me a $40 damage charge when I move out.  The dark black crud is just burnt on food which, if I really wanted to, I could scrub it off with a brillo pad.  The light brown stuff is a stain in the surface which so far I have found nothing that would get rid of it. 

I would love to see if anyone has been more successful than I in cleaning their drip pans or if this really is a useless waste of energy as everyone tells me.

I have found this blog for WD-40 but am nervous to use it given drip pans are  where the heat is applied and something about the combination of noxious fumes and chemicals around my food just doesn't sit well with me.  If it is a last resort thought, I will try it, even if it is just to throw the pan out when I'm done.