Unique Keys on Corrupt Serial Fields

I have a customer who (somehow) got duplicate values in a SERIAL field that is keyed uniquely. I need to figure out a way to rebuild his data file and make the values in the SERIAL field unique. I have tried DROPping the column, ADDing it back as type integer, then MODIFYing it to type SERIAL but the data in the column is still not unique. I don't want to UNLOAD the table, write a program to change the serial field's value in the unloaded ascii file to a unique number (record number), and then insert the data back into the data file, unless that is the only way to do it. If I could simply do something like this: alter table univ drop (un_sys_no); alter table univ add( un_sys_no integer); update univ set un_sys_no = [some unique value [record_no()?]]; alter table univ modify( un_sys_no serial NOT NULL); my problem would be solved but I don't know how to set a unique value into un_sys_no after it as been dropped and then added. Any help would be greatly appreciated! Thanks.