Thank you for your post, and I apologize for the late reply.
The "Perform Find/Replace" script step gives the user the ability to specify searching across all records or the current record, as well as across all fields or just the current field. If you select the current field, you must ensure your cursor is active in that field. This can usually be accomplished with a "Go to Field" step just preceding the "Perform Find/Replace" script step.
This allows greater control as you can specify the exact field contents you want replaced.