Hi,
The security policy sounds right as the application junos-sctp-any is IP protocol 132, i.e sctp.
Apparently, an sctp profile is also required in the security policy configuration but am not sure its configurable:
http://www.juniper.net/techpubs/en_US/junos12.1x45/topics/example/gprs-sctp-profile-configuring.html
security-flow session output indicates the application hasn't been detected as sctp.
Do you see any security-flow session for the return traffic by matching source-address of server for instance.
Would you have an idea of the payload size expected. Also, can you confirm the traffic reaches the server/destination.
Cheers,
Ashvin