My 5yo pushed in a SD upside down and it bent the WP pin beyond repair. Nintendo uses Mitsumi CIM-J44N slots. these slots have normally open type contacts for CD en WP. http://www.mitsumi.co.jp/latest/Catalog/... so if no card is insterted, or write-protected, the contact is open. Since the pin was heavely bent (in my case), there was no repair possible to the pin. I pulled out the pin, and buzzed out the motherboard. The WP (write protect) and CD (Card detect) lines have jumper pads on them. So i just put a solder blob on the WP line jumper, and now it always reports as not write-protected. (who needs WP anyway?) Quick and easy fix.
I would never run an injector/engine cleaner. It might loosen carbon buildup en cause extra wear or loss of compression due to engine age. Best way is to get them professionally cleaned on a test bench, and have them flow tested. Most companies that do refurbishing and sell cleaned injectors will give a reduction when you trade in your old injectors.
Did you use original foam tape to adhere the digitizer? Or double sided tape? I've had the same thing happen to me on my first lumia 625 job, using self cut double sided tape. Since then i always have original pre-cut foam tape in stock. Not had a problem ever since. the sensor is very picky.