In the good old days of Fiat, their engines leaked oil, so did their Fwd gearboxes. This covered the front subframe in oil, so stopping the rot. Stones and bolts, nuts and other road debris still pepper the sump on some models.
But again, as you have found out, non oil leaking Fiats do rust.
The wife's 2012 Punto, had two sumps put on it. Even though when she first purchased it In August 2012, I cleaned the front of the sump and bottom and put on a spray of underseal/bitumen.
That's a bit of a crack there, can't disguise it with anything, as it's a stressed point with a bolt in it.