Cylinder does not lock on all chambers (36-1)

[zinj]

Inspecting a 36-1 that I have, I found that two chambers unlock when hand-rotating the cylinder clockwise (i.e. in the opposite direction of normal travel). What is the solution to this problem? The cylinder locking mechanism seems to be in good condition (it has no rounding and seems to engage all cylinder lock notches well). Is this some parts replacement can fix, or will this gun have to go back to S&W?

 

[500 Magnum Nut]

Should not unlock just by turning the cylinder. The cylinder stop and spring need to be looked at.
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