My 642 came with a lock. I heard the stories of failures, though I never seen evidence or conformation they occur I figured why take the chance.
I couldn't see a reason to ever use the internal lock so I just removed it.
When I got mine there wasn't an option of a no lock 642, or at least in the area I lived.
I don't care about destroying the future value of my 642, I got it for a carry gun not an investment, so I don't care if I still have the little key hole, and I don't have to worry about whether lock failure is true or not.
I guess its an individual thing.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071