A very large British 747 Classic operator used to do standard full (30) flap landings instead of 25 flap. About 20+ years ago, flaps started falling off, and a Boeing team came over to see why only one very large British operator was so affected. They were not impressed as Boeing were designing the machine for standard flap 25 with 30 available for special circumstances, and stressing the system for that.
I believe the 737 up to -400 was designed this way, with mainly flap 30 intended to be used. It might be worth checking the Boeing manual itself to see if perhaps one of the airline management team is allowing a personal preference to override the manufacturers intention!