If you do a search on "goodwill" or "gw" letters you'll find lots of success stories. Many people have had good outcomes.
Some have had good/bad experience.........good/bad meaning they asked for lates to be removed and the creditor removed the whole tradeline. Depending on what else is on your report, this could be a good or bad thing.
Here is a thread with a sample GW letter and some discussion of GW letters -