Key locks like the S&W's now have are a solution to a non-existant problem.
It was put there as a feel good add on so that S&W could sell guns in areas that require integral locks.
I hate add on locks and safetys, I won't buy a new S&W, Taurus, Rossi, Remington, Winchester, et al.
Like one of the above posters said there are too many older guns to buy to even wory about it.
However here is a solution to the "locked-unlocked" wory that many have.
DISASSEMBLE the revolver. You really don't want to do this with it assembled. Too much of a chance of getting Loctite in the action.
Clean the lock with break clean or something to remove all the oil from its working parts.
After the lock is degreased, put it in the "OFF" position and put a couple drops of "RED" Loctite in it.
Once this cures there is no way in the world this thing will move without heating it.
Reassemble the gun, wipe it down and your done.
No gaping holes, no gunsmith modifications, and essentially NO safety to accidentally get turned to the "ON" position.