Mainly 1.25 GHz models suffered from leaky caps. You can look at the caps next to the RAM to see if they are bulging. Apple will still replace these boards for free as long as they still have boards in stock. When all the boards are used up (or 5 years after the eMac was sold), it's over.
Apple stated somewhere that they only keep parts in stock for 5 years (7 years in California). Perhaps after 5 years they send the remaining bits of stock to California, but what happens to the remaining parts after that?