As mentioned the place to be concerned for frame cracks is inside the yoke cut under the barrel ( the part of the frame the barrel screws into)
It seems to be an issue across all ages of these guns and while I agree these should be standard pressure ammo only guns, the general consensus is these cracks are NOT related to shooting but issues with the barrels being torqued into the frame.
Age or general condition of the gun is NOT a way to determine crack risk . It is not unheard of for guns that are or look brand new in box to have th3 crack, and others carried and shot extensively to be fine.
While I have been interested in a model 12 for some time , my general rule is to only consider purchasing one I can personally inspect ( with bright flashlight and magnifying glass ) to confirm no frame crack. So far I have not had a chance to come across one in person at a decent enough price.
To a lesser degree, the same issue occurs in J frames as well.
In some cases the crack is so fine and so straight people think it is normal .
I read a report of a cop in an agency that used alloy frame 38’s for bugs, department issued. After the RO’s gun developed a crack, he had all the troops carrying alloy guns to hand them over for inspection. About 25% of the guns in service had frame cracks