I am looking to replace the keyboard only or the TOP cover of the a1278. MBP mid 2012. Discussing with a Genius bar tech guy, he recommended to buy the Top cover including the keyboard and backlight, apparently. I found the top cover for 39 CAD+ transport. While the Keyboard only can be bought at +/- 10 CAD + transport. Hope this helps. PS: I think I will go for the TOP Cover, less risk with keyboard and backlight, power button too.

I can testify, the I/O from the DVD slot (2nd SSD disk) is hugely slower.

After reinstalling Mojave on the primary disk (typical SDD / HDD slot) the transfert of the data and applications from the 2nd disk (in the DVD slot) to the primary SSD disk took...... 5 days ! to transfer 550G.

Finally I have my mid2012 now running Mojave (32 and 64 bits - and have the possibility to run my old 32bits APPS too) which I won't do any upgrade anymore and 2 disks of 1T.

It's pushed to it's max. :) ... and works.

Yes it takes time, but worth it.

Good luck.