I just replaced the latch plunger that goes into the front of the ejector rod on my 629-1. I think the new latch is a MIM part and it fits much tighter into the end of the ejector rod.

The MIM part is all polished and smooth where the stock part is roughly ground. It reduced the side to side cylinder play quite a bit. It's cheap and I may do it on more of my Smiths.