-I option does not work for Junos with OSPF v3
Junos publishes some strange interface identifiers in the ospfv3NbrIfIndex column in the table OSPFV3-MIB::ospfv3NbrTable that don't match with identifiers in IF-MIB::if(X)Table. That means that the -I/--interface option does not work together with OSPFv3 (the -3 option) for Junos devices.
We should ask Juniper what the interface id refers to, and have a Problem Report created if they can't give a good answer. If they have some way of mapping it to an interface name, but which isn't standard, we should consider adding a vendor quirk workaround for it in check_ospf_nbr.