A lost cause or worth a shot?

I went a bit mad last weekend and changed the oil in my lawnmower.
Unfortunately, I didn't realise just how far hot oil could splash and
managed to spatter my craghopper trousers with old oil. Conventional
washing hasn't shifted the oily marks.

Any suggestions or should I just bin them? I haven't tried drycleaning
(yet) as I'm concerned I could be just wasting my time (& money).

Tim