I have a C-172 on leaseback to a Flight School. I have been replacing DG's about every three months. They are not using it for "spin" training, just normal Privat/Instrument work. Out of 5 C-172's, mine is the only one going through DG's. The C-150 that used for spin training has not had one fail yet. The suction is in the green at cruise power. All the filters get changed every 100 hours (I usually do all the 100 hr Insp.).

Any thoughts?