Diesel has kerosene in it. I have been able to use non-volatile parts solvent (Napa Auto Parts etc.) on an old white T-shirt (NO graphics) and scub like heck.
After I did this with a couple of t-shirts, rotating so not to grind in the stuff I was "thinning" out of the carpet, I let it dry. I then used straight Simple Green and scrubbed again. After "washing" that out with multiple dish towels and blotting it dry, I used Resolve spot and stain remover liberally with another couple of t-shirts.
Once this was done, I used my wife's Bissel carpet cleaning machine and this HD traffic and stain solution.
Carefull as most stain removers that clean oil etc are a mild acid base so be sure to follow directions.
This did the trick and the carpet looks and feels like new.
On a side note, you could contact a professional "commercial" cleaning company like "Clean Pro USA" and ask them.
On a side note, as a boy, I managed to get some epoxy based motorcycle gas tank sealer all over my parents wool carpet (don't ask)
. One of my brothers worked for Host Cleaning Company (they did hotels) and he came and got it out...completely...and it was hard enough to drill with a steel drill bit.
Good luck and let us know how it turns out.