Reciently we faced an issue where SQL Server was on SP2 ( clustered Enviornment) and we were not able to install replication ..This is fairly simple on a standalone machine but not on cluster ..
If you try to achieve it through ADD/Remove (appwiz.cpl) program you may get this error : The Installer has encountered an unexpected error. The Error code is 2819 .ControlProductclash1 on dialog Product clash needs a property linked to it .
The solution is to use the commandline setup ..we tried several combinations untill this was successful :
start /wait setup.exe /qb VS=TSQL31 INSTANCENAME=TSQL31 ADDLOCAL=SQL_Replication
Now , Replication is installed but its on RTM :) ...you still need to apply SP2 ..
Moreover , any CU after SP2 will fail as Replication bits are on RTM ...
use the same command with hotfix name instead of setup.exe