1000psi no rinse agent, flex with citrus solve, rinse thoroughly, speed dry, do not dwell on one spot. And if its really bad scrub with brush pro 20 before you extract, dwell time is 15 min putting the flex down hot.
It was a trial job for a buddy...thats the tool I had with me at the time....yes it was GooeyWhew!, must have been real bad to have to blast it with that single jet tool..
What else did you try?