Wow...there were official strategy guides? Huh! Never knew that.
Red Key to the MonsterReturn through the Yellow Door from where you just entered. Go left Through the Red Door into the four-part Monster chamber (I in Fig. L7-12). Kill the Monster.You may have to replenish your supplies from the weapon storage bays in Area J (in Figs. 27-11 and 27-12). When you have killed the monster, escape the mine through the exit located in the room's ceiling.(K in Fig. 27-13).
The walk through for the final boss battle in D2 makes no mention that the boss is only vulnerable in one spot.
The bulk of the guides are filled with fluff, back stories on each map/mission, back stories on each bot, etc...