Thanks to your help, I've discovered I need to increase the size of my mdb MaxSize. I created the following LDIF file to increase it by a factor of 10:

dn: olcDatabase={1}mdb,cn=config changetype: modify add: olcDbMaxSize olcDbMaxSize: 104857600

Now I can make changes to the LDAP directory itself, but when I try to make changes to the OLC data, like this change, I get an Insufficient access error:

$ ldapmodify -v  -f mdb.ldif add olcDbMaxSize:     104857600 modifying entry "olcDatabase={1}mdb,cn=config" ldap_modify: Insufficient access (50)

How can I overcome this and give myself access to make these changes in the future? In the past I was advised to do a slapcat of the OLC database, make my changes, and then do a slapadd of the modified LDIF file.. Unfortunately, I forget details of that magical incantation, and I'd also like to make so I have the necessary privileges to make these changes in the future through LDIF changes like the one above.

All you help is greatly appreciated. I know these answers are probably in the manual, and "RTFM" might be justified, but I'm a little under the gun trying to get a formerly working system up and running again, and I still haven't fully grasped OLC yet.