Let me tell you about a great solvent. This you will find at auto parts stores, such as Advance Auto (where I bought it).

Blaster Penetrating Catalyst.

You can get it in a spray can, but even better, it comes in one gallon cans. My gallon can came with a spray bottle to fill up for daily use.

This stuff is really effective and inexpensive. You should give it a try. Here's a link: http://shop.advanceautoparts.com/p/blaster-penetrating-catalyst-128-pb/7040062-P

Curl