Are you using distilled water to fill the cooling system? If not, Miami city water is LOADED with salts, so you will have corrosion and plugging problems.
I don't think you will be able to get more than a reverse flush on an aluminum rad -- never seen one go back together and seal, they usually break off from fatigue. Better to get a new rad, flush well (nothing you buy over the counter is going to touch the crud in the rad), then fill with Xerex G-05 or MB coolant and distilled water.
Miami is hell on cooling systems.
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!