Hard to Clean Carpet

We have a tan carpet. One area of the carpet is walked on very often. Over the years, it became difficult to clean via normal carpet cleaning methods. I have used "Resolve" (carpet stain cleaner) and I scrubbed a small section at a time each day. This has made an improvement, but not the ideal results.
Does anyone know a technique or product that may work better than "Resolve"?
Thank You in advance, John
PS, Remove "ine" from my email address
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