How to fix a water leak, drivers side door seal is said to be bad.

What is your question?

A couple weeks ago, after washing car, discovered water pooling in the drivers side front. No water running down inside of door. Thinking drivers side door gasket is bad. Can this be fixed at home with minimal repair skills or this a big deal. Also need to know what parts to get. Dealer wants to do the job, I think $500 is ridiculous.