Respectfully, I still believe the clean up (after moving the body to the back floor, or temporarily removing it from the car) was done prior to gassing up and prior to the trip up Larch Mountain. Just far too much risk to pull into an attendant-served gas station with a car full of blood, etc. and the window gone. For someone to have been shot at point-blank range 4 times in that front seat...well, not to get too graphic, but the amount of traumatic evidence visible through that open window would have been tremendous, and alarming. (Remember, the description we read about, bad as it was, was what was visible AFTER the clean up.) No way I'd have risked driving into town with an open window and meeting with attendants at more than one gas station without at least a cursory clean up.
There'd be no need to clean up a hopelessly bloody car on the mountain prior to abandoning it at the far end of a well-lit, well-populated, 24-hr-video-surveilled parking lot. He wasn't trying to keep the car from being found, in other words. And he wasn't trying to keep it from having blood evidence for LE in it, as he obviously knew he hadn't cleaned it up thoroughly enough to prevent that finding. (I'm sure he saw the 2' x 3' pool of blood on the floor of the back seat when he pulled the body out.)