28’s of that era did have bolt on lead keels. Ours was an 85 and was the same way. 3’8” was considered the shoal draft. They also made a full draft that was about a foot deeper. The lead is coated in some kind of barrier but over time it’s not unusual for that to chip away, especially in spots that have imperfections in the casting. If that happens it can be repaired by sanding or grinding down to fresh metal (with significant PPE) and coating in new barrier coat.
I haven’t heard about any significant problems with the bolts. You may read about O’Days having problems with thin layups in their keel stubs, but that only affected the 3-digit O’Day models in the later 80’s.