Be very careful about this. The shop may "boil it out" and it may look fine when you pick it up. But, hold it up to the sun and you will see all kinds of crap in the fins. The radiator won't perform any better after you have shelled out $75.00 or so.

In discussing this with the local shop here, they advised that I go and get a pressure washer to blow all the crap out of the fins. Apparently, they had no means to accomplish this.