My Old man used to throw in some diesel fuel or kerosene in his tractors/dozer tanks when the tanks got all scummy along with a bunch of small rocks, nuts, old ball bearings, whatever he had around and shake the pi$$ outta them, or toss them into the bed of the truck for a week or so while he drove around, then just dump it out on the driveway (Gravel), and repeat if it was still filthy.
Don't think the Spotted Owl huggers would go for that today, though,

But it worked! (Someday, his driveway is going to be declared a toxic waste zone, I swear)
X2 on the radiator shop tho. If one won't do it, another, that knows what they are doing, will. I think everyone could use the work right now.
Ray