Reference the action problem and to help isolate the cause....when you get the grips and sideplate off you might try temporarily removing the hammer block, then replace the sideplate and try the action in the positions you describe...."sideways" and "facing down". I've had instances where the flag on the hammer block interfered with the trigger return when the flag at the top of the block lightly touches and drags on the hammer as it (the block) is trying to interpose between the hammer face and the frame during the trigger return phase. If this is what's causing the problem there is a relatively easy fix.
I have read threads on the forum where members describe broken hammer blocks in this model...not sure of the cause. I've never seen one break in 40+ years.

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Ret. LE, FA Instr, S&W Armorer