This may not be exactly what you are looking for but it was an easy fix for my situation. I have a Broadcom chip also.
I made several persistent live USBs that allowed me to have the traditional menu and a working wifi. These persistent USBs were made using UNetbootin and I initially made them with 2048 Mb storage. Later I remade the 18.04 stick using the newly released MATE 18.04.2 ISO and with 8192 Mb storage.
See - Edit livecd iso to have traditional menu for visuals. Files and a gtk setting were obtained from data4 and mate 18.04 partitions. Files in ~/bin were edited to allow working on the persistent USB.
I updated this last USB drive, the updates were few. I installed firmware-b43-installer, dconf-editor, conky-all and synaptic. I used MATE Tweak to change the panel to Traditional and get the old Application, Places and System menu back. Moved firefox to panel center and added mate terminal, gksudo and conky toggle shortcuts next to the menu. I copied .config/gtk-3.0/gtk.css to the persistent drive which shrank the distance the tray icons took up. I added a shut down button, but the displayed time was (I guess) zulu time instead of local due to being a live USB.
Good luck nemo.