one of my Austers was used for crop spraying for about a year.
far from causing lots of hidden corrosion issues it was actually the making of the old girl.
when they gave up on ag spraying with the old girl the lame stripped back the entire underside, sorted it out and put new fabric on.
when I came to bead blast the entire airframe about 10 years ago there was not one skerrick of corrosion on the underside tubes of the aircraft.
crop dusting around Colleambally in about 1965-8
redone about 1968
beadblasted and found to have zero corrosion 2000
so dont write off a tiggy that has been used for ag spraying. it may not have harmed it at all.