Unhappy Nexus 7 bootloader issues (unable to update to 4.23)

So this is kind of a long story but basically I had a Nexus 7 8GB model. I bricked it by destroying the bootloader and so I sent it back for RMA.

When the thing came back it worked but was laggy as hell. I did all the normal erases and whatnot, even flashed back to stock, still laggy. I figure the EMMC was toast. So I purchased a used Nexus 7 16GB motherboard from ebay.

The new motherboard worked but came encrypted so it booted and asked for the password. Of course, not knowing the password, I had to get into recovery and do a data reset. After all that I was able to root and a Cyanogen mod based ROM.

The problem I currently have is this: I am unable to flash or update the bootloader which is stuck on 4.13. When I try and push the kitkat bootloader via fastboot I get "BAD PARAMETER" and am unable to get passed this.

In case anyone cares I was able to follow the bricksafe flatline procedure and captured the existing bootloader partition blob which is now saved to my computer. I have tried to push that bootloader back to the device and that works but I CANNOT flash the damn 4.23 (kit kat) bootloader.

Basically my Nexus 7 charges at a snails pace now but works. Any help is very much appreciated!