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No “Rebuild Search Index” showing on version 188.8.131.52
1) Try deleting everything in your magento/var/cache folder and your local browser cache (close and reopen)
2) Are you running any extensions that were based on a previous version that need to be updated / removed?
3) How did you upgrade, via Connect? You could check to ensure all folder permissions are correct (so that Connect can overwrite) and attempt the reinstall option from Connect.