2003 Ford Mustang Sticking brakes

Dear Carpros.

I'm having a problem where my brakes are sticking. The problem is mainly with the front left caliper but the front right is also sticking slightly.

I have tried a couple of things. For instance, I've fixed the sliding pins and I have had the brake calipers restorated by a company nearby but nothing seems to work.
My thoughts at the moment are that there might be a faulty brake line or perhaps the master brake cylinder is in bad condition?

I would be very glad to hear your thought on the matter!
Thanks in advance.