You’ll find the preventive maintenance checks for the M320 grenade launcher on Page 0019-2 of TM 9-1010-232-10 (Nov 08, w/Ch 1, Apr 12).
The BEFORE PMCS’s Equipment Not Ready/Available If section for Item 1 tells you the weapon isn’t ready if you see cracks, excessive wear or corrosion. But now TACOM has provided new PMCS guidelines.
The area where the vertical locking lever contacts the receiver is exempted from this requirement. So there’s no need for turn-in with this exception. Only turn in your grenade launcher if a deformed area or excessive wear prevents the vertical locking lever from latching firmly onto the receiver.
Keep an eye out for a future TM change that adds this update.