CMS 16GB (2X8GB) DDR3 10600 1333MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Lenovo® Thinkpad T520 4239; 4240, 4241, 4242, 4243 - A13 at Amazon.com
8GB Stick for IBM Lenovo ThinkPad T Series T420 T420i T420s T520 T520i. SO-DIMM DDR3 Non-ECC PC3-10600 1333MHz RAM Memory. Genuine A-Tech Brand. at Amazon.com
Lenovo Thinkpad T520 Disassembly video 4K, upgrade RAM & SSD, take a part, how to open - YouTube
Arch Memory 4GB 204-Pin DDR3 1333 MHz So-dimm RAM for Lenovo ThinkPad T520 4240-4AU at Amazon.com