internal engine sludge cleaner

What is your question?

I have a 2003 grand marquis with a little over 100,000 miles and all is fine. However, the shop where I take it which specializes in fords and has a great reputation suggested that I purchase (for just $12.00) a can of cleaner which you pour into the engine just like you do when you add oil and then let the engine run for a while (I cant remember how long he said to let it run but I think it was for a least an hour) and then you drain the oil, change the filter and put new oil in without any additive, so basically after draining the oil with the additive, you are just doing a normal oil change. The product claims to get rid of harmful internal sludge etc. and the shop owner says they have used it for years without any trouble and that you can see how dirty the oil is once you drain it. Any knowledge on this subject? Thanks in advance. Todd