Kevin Hill goes into detail on what DBCC OPENTRAN does:
I have verified that new records I inserted have been read by the log reader, AND distributed to the subscriber(s). This means that while you are seeing
Oldest distributed LSN : (37:157:3)
There is not an error…just info.
If you have non-distributed LSNs, there is something to troubleshoot in the replication process which is way outside the scope of this post. A non-distributed replicated transaction/LSN CAN cause some huge Log file growth, and need to be investigated. If this happens frequently, use the TABLERESULTS option to log to a regular table and alert on it.
Good information here.