My 2004 Sienna is like that with food crumbs all over, I just vacuumed it for now thinking I would get the rest later by blowing it out with compressed air, later is not here yet and I am parking it out of the rust belt for winter so the mice may get a treat if they can get in it. Rest of the story is probably pretty common, parent drives new van for many years than gives it to their kid, who neglects it as free stuff is usually never fully appreciated, dealer takes it in on trade, cheapskate shade tree mechanic tries to buy as cheap as possible being the drip at the rear of the motor is known to all who look there.
Finding the gas additive Star Tron Enzyme for the lawnmower/snowblower gas can is about all I was working on today, neighbor cleaned the end of the driveway so I had just enough gas to do the rest, but I am not going anywhere being the roads will be wet and sloppy-est today and after cleaning the snow I am sure to reward myself with effortless task for the most part.
Your post reminded me of a good YouTube dent repair video of the tear down on a Buick SUV, worth watching for those of us who might get into this kind of cleaning or maintenance repair.