My best recommendation - get another same male unused connector, cut them and re-wire. :)

1. Two slots as a pair. Stock configurations are 2x2GB. Best to upgrade as a pair. I have the same model as yours which I have used 2x 4GB. 2. Just a normal DDR3 1600MHz will do. I'm not sure about where to get it in the UK though. I'm using this currently. (image from Google)

There are diagnostics LEDs instead. Near to the PSU connector. From bottom upwards - 1. Indicates that the computer is turned on. This LED will be ON as long as computer is turned on. 2. Indicates that the computer is turned on. This LED will be ON as long as computer is turned on (but is not asleep) and power supply and voltage regulators are working correctly. 3. Indicates that the computer and the GPU are communicating. This LED will be ON when computer is communicating properly with the GPU. 4. Indicates that the computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED 4 is ON and there is no image on display, then the LCD panel or the cables between LCD and logic board might be installed incorrectly or need replacement. A. Diagnostic LEDs B. Real-Time Clock (RTC) Reset Pads C. Coin Battery Voltage Test Pads Phew. Hope it helps.

Is there any chance you've "accidentally" enabled 'Show Touches' in the Developer Options?

Have you verified with Apple with regards to the Quality Program? Make a trip down to the Genius Bar and verify whether your unit is still eligible for the FOC replacement.

Try isolating the RAMs, Hard Drive and the WiFi Card. If it still persists - it might be the logic board.

That Side A is faced inside. So that so called 'Teeth' is facing you.

Just that thin single line? Is it visible before the Apple logo? If it does - go get the Display replaced my friend.