I may be mistaken, but I believe the recall problem was with certain 357 mag loads (Federal, maybe others?) flowing primers back into the firing pin hole (not just a general backing out), they made a bushing with smaller hole and tighter fitting firing pin to alleviate it. I dont think it should be a problem with 38s. I think this is also about the time they started toning down factory magnum loads. Wonder if its a coincidence?
Several guys here may know more about it, @Wayne Dobbs @Outpost75
If the recoil shield is allowing primers to back out more than normal, you should be able to see it inset below the rest of the frame surface. Theres enough room for it to happen when everything is correct, but the primer usually re-seats itself when the case comes back. its NOT a zero clearance situation. Try firing just primed cases in a normally functioning Smith and it will probably lock up. So is it just backing out or are they flowing back into the firing pin hole, the term often used is "cratering" the primer.
Do as you wish if it truly needs the fix, Im not positive they all actually needed it, I think it was done as required and guns checked and in spec or modified were marked. Id prefer someone other than the factory to work on it if it were mine. I have no intention of sending anything to the factory for any reason at this point.