OK, since my last correspondence, things seemed to be going OK.
All changes had been replicated perfectly until last night, I deleted one record, and it only deleted on 4 of 6 of my servers. I removed it manually from one of the other two 'offending' servers. The last one then deleted the record on its own.
So it seems as though SyncRepl is highly flaky. I looked into the firewall timeout issue and determined that it is not the cause (if it were, this issue would be happening every 30 minutes (default firewall timeout for the LDAP service)).
We're still using the accesslog DB for write-transactions.
Jeff