Aircraft Instrument Systems Which of the following instrument discrepancies would require replacement of the instrument? 1. Red line missing. 2. Case leaking. 3. Glass cracked. 4. Mounting screws loose. 5. Case paint chipped. 6. Leaking at line B nut. 7. Will not zero out. 8. Fogged. a. 2, 3, 7, 8. b. 1, 4, 6, 7. c. 1, 3, 5, 8.