The primary funciton of seals on a rolling element bearing is to effectively exclude dirt, grit, moisture, and other substances which might harm the bearing during normal use. More often than not, a sealed rolling element bearing has shields on both sides and is pre packed at the factory. If the front bearing only had a shield on the inboard side, its function would have been to reduce contamination to the bearing. Installing a bearing without shield(s) leaves it open to the elements - a condition that the original GM designer must have been concerned about. I'd put the original style bearing back in. Someone was concerned about contaminating the bearing and spec'd out the shield.