One of our clients used the Oracle Webcache and Imperva WAF, and when their key employee left, no one else knows how to configure or maintain it. Since the webcache was no longer supported by Oracle, which is not PCI compliant, we came in and replaced it with the F5 load balancer and replaced the Imperva with the ASM module. It was easy to configure and the client was happy that they were PCI compliant again. I wrote the top 10 questions to PCI compliance on my website http://www.moreprocess.com/process-2/top-10-questions-to-pci-compliance