Diplomatic Approach: I've “fixed” (Diplomacy vs. 18) to (Diplomacy vs. MD), which I think is correct based on the action's description.
Rallying your Crew: I'm not sure I understand this check at all. IIUC, you first do a Diplomacy check against 0, and then, if successful (always except with a 1,1 roll), you do a hull check to increase morale. If you want to have some bonus for the hull check, you can roll the Diplomacy check versus a higher number (vs. 3 for a +1 bonus, vs. 6 for +2 bonus, etc.). Is that so?