@Kopfpalme I build a uboot-r/w version lede, you can use it and mtd command to flash the uboot.
- Download this lede and flash it in luci.
- Download new u-boot to /tmp as uboot.bin, cd to /tmp in ssh.
- Flash the uboot by command
mtd write uboot.bin u-boot - Flash Openwrt 18.06.1 in luci.
@JuggernauT To be honest I dont have soldering skills 
, that's why I use conductive paste. It's more like writing something by a pen.
I use two needles to make a tiny and thin conductive paste wire, put it between the two rx solder joint, then use hair dryer make it cured.
The most difficult part is, the two rx solder joint is too small, which will requires some craftsmanship. If you put conductive paste in wrong place or make it diffusion on board to connect to other element, you need clean it and try again.
And set the hook also need some practice, but acceptable.