hmmm...
if this frame had cracked, there would definately be marks of the crack/repair on the rail above the hole, which i can not see in this picture. when i got my tormented and beaten to death 5904 tcfxxxx, after i cleaned it up and replaced the springs and broken wraparound grip, i went on and fired it. the pistol fuctioned fine, but! the slide would not lock open, plus the slide release would hang to the side of the orange plastic magazine follower, not allowing the magazine to free drop when released. i had to pull the magazines ou. (new and old magazines) at first glance, i figured, easy fix just replace the slide release lever. upon inspecting and comparing the said lever to my other 59xx such levers, ther was nothing wrong with it, (????) interchanging the levers, the problem remained. further inspection then revealed the real issue. the lever had a very small play in the area where yours is repaired, as that hole was a bit bigger than it should (like half a milimeter, not more, but enough to raise this issue). and here is the weird part. i inittialy thought this hole was woalloed out due to excesive wear, and or the aluminum frame being weaker than steel and so on, but no! the hole was/is perfectly round. just a bit bigger. my test repair to my this finding, was i scizzored a strip of tin from a tin can, and placed it just in the fashion yours is done. no glue, no permenant stake no nothing. the slide keeps it from rolling, the lever from walking out. guess what. 5 years and about 3k rounds later, the gun has functioned flawlesly. so in the end as we say in Greece, nothing more permenant than the temporary. lol. my take on this frame you have, is that they had the same problem like i did, but they also had access to more elaborate machine tools than my scizzors and tin can. my advise to you, shoot the gun and enjoy it. these pistols are so strong, they will outlive us all.