Rob and Jason's desire? (6)
I believe the answer is:
fleece
I believe this is a double definition.
'rob' is the first definition.
(synonyms)
'jason's desire?' is the second definition.
(Jason stole the golden fleece in Greek myth)
'and' acts as a link.
(Other definitions for fleece that I've seen before include "Charge way over the odds" , "Diddle" , "Sheepskin - take to the cleaners" , "Woollen coat of sheep" , "Jason sought the Golden one" .)