As im sure you know diesal is very difficuly to remove especially the smell but i have found a generic product called "Traffic Film Remover" or even a general wheel cleaner should work well. They are water soluable and designed to desolve oil, grease and tar. I use it to clean just about anything - works well on my kitchen carpet and removes fat and oli splatters!
AKA "Truck wash". You dilute it about 4:1 normally but for tough jobs just use it neat applied with a pump-up sprayer. Keep away from paintwork! Apply, leave for 2 minutes then jetwash the mats till the water runs clean
If you can't find it locate your local professional valeters and ask them
Is generally considered to be the best source among professionals. We have the whole interior cleaning set including handy-wipes and orange-based hand cleaner.
S211 E320Cdi Avantgarde Estate & Toyota Land Cruiser
Errrr well there is theory that Coca Cola will remove diesel pong from fabrics but then I suppose you have to get the Coca Cola stain out. Test that on something you do not care about first!
Having spoken to SWMBO suggested that you wash the afflicted part with a strong liquid detergent solution, rinse well, and then use something like Vanish Carpet cleaning spray.
Thanks to everyone who has replied. Havnt come across the "Wurth" product range Miro but will keep a look out now. Sounds good and recommended by Mercedes I notice.