Advised yesterday when had "B" service with 16,900 engine seal was leaking.

What is your question?

This is correct mileage. Purchased in Nov 2007 and there are no leaks on garage floor and only had to add about 1/2 qt since had oil changed in May 2011. Was advised there is a "pan" that kept to oil from showing on floor. Is this a common problem and what happen if do not replace the seal. What's approx cost for this. Thanks Doyle