The German P-38 of WWII had a steel frame.
However, the P-38 was also produced after the war with an aluminum frame up until 1995.
The P1 is nothing more than the aluminum P-38 as marked for the West German military.
Frame cracking in the aluminum guns is caused by a very high round count gun, or shooting hot ammo, heavier bullets than it was designed for or using "extra power" recoil springs.
These guns were designed for standard loads of 125 grain ammo, and work with 115 grain.
Heavier bullets, hot ammo, or stronger springs can cause cracked frames, slides, or broken locking blocks.
Later P1 guns have a hexagonal pin in the frame in front of the trigger. Contrary to popular belief, this wasn't to prevent cracks, it was to give the locking block a "wear surface" to operate on.
They found that high round count guns would wear the aluminum frame in the locking block operating surface and the guns would give locking problems.
To allow military guns to shoot much higher amounts, later P1 guns also had a "'fat slide" to prevent slide cracks.
In other words, if you shoot standard loads of 115 to 125 grain bullets, the P1 will last probably longer than you will unless you intend on shooting MANY thousands of rounds.