300E coolant leak

I've read many posts on the subject, but where exactly is the water pump located? I found a small puddle of coolant under the brake master cylinder, and a small amount on the garage floor (behind the left front wheel well). Is this in fact the pump, or could it be a hose? It appears that removing the pump is a difficult job. Is it very expensive to have it done? I would appreciate some advice. Thanks!

Brian