John Driscoll, whose book should be on the shelf of every ad/promo professional, has a great tip on his website for searching OPDP's database of enforcement letters.
Instead of entering a phrase such as "FDA Warning Letters" + company name or brand name + issue you want to research, use this link , which is also on John's website.
Then just replace the word "misleading" in the first part of the search for whatever issue you want to research (e.g., "patient testimonials" or "comparative claim" or "peanut butter").
That will search most OPDP/DDMAC letters since 1997. There's some finickiness because the OCR isn't always flawless, but it's a much better search technique that starting from scratch.