saving replication latency for monitoring purposes

I have SQL 2012 enterprise edition, transactional replication. many servers, many DBs.

This morning I come to the office and been told the latency on some databases was about 30 min behind.

I have a look through replication monitor and all is normal now.

I currently dont monitor anything about replication, so I dont have anywhere to look for past issues.

What should I be saving regarding replication, so that I would know what caused the latency and which tables, DBs?

Does anyone has a script for sharing regarding this?