Prashanth, responses to your questions :
System UpTime: 214 days 21 hours 50 minutes 19 seconds (for the stack)
Yes the stack was synced during the last maintenance window. But I've seen that the slot 2 have reboot during the last months many time for unexpected reasons. Here the log of the last reboot :
08/24/2015 01:06:05.88 Slot-1: Module in Slot-2 is operational
08/24/2015 01:06:01.33 Slot-1: Done synching ACLs to Slot-2
08/24/2015 01:06:00.87 Slot-1: Synching ACLs to Slot-2
08/24/2015 01:05:40.07 Slot-1: Slot-2 being Powered ON
08/24/2015 01:05:37.05 Slot-1: Module in Slot-2 is inserted
08/24/2015 01:02:55.57 Slot-3: Slot-2 FAILED (1) Not In Sync
08/24/2015 01:02:55.56 Slot-3: BACKUP NODE (Slot-2) DOWN
08/24/2015 01:02:54.07 Slot-1: Slot-2 down, resetting all TCP connections to it
08/24/2015 01:02:54.07 Slot-1: Module in Slot-2 is removed
08/24/2015 01:02:53.48 Slot-1: BACKUP NODE (Slot-2) DOWN
08/24/2015 01:02:53.29 Slot-1: Slot-2 down, resetting all TCP connections to it
08/24/2015 01:02:53.29 Slot-1: Module in Slot-2 is removed
I'm not aware of changes in the last months, I've checked the show debug system-dump and nothing is present. We'll try to resynchronize the slot next Sunday, I will make a feedback when it's done.