The problem with landing with one of the main legs not locked down was driven by the overall configuration of the a/c. Due to the relatively high wing coupled with the sweep back, it was thought that as the wing tip of the affected side contacted the runway there was a strong likelihood of the whole thing cartwheeling.
Re the fires, one of the problems was indeed burning through the control rods that ran to the hydraulic motor for the tailplane. If I recall correctly, initially these rods were aluminium and burned through quickly, when the fleet went through the 'Fast Fire Mods' programme, among other fixes these rods were replaced by steel items, the rumour was that the burn through time went from 9secs to 13!