The sealant is like tough RTV and you would need to redo it each time. If you buy some, the tube is the size of a medium tooth paste tube so you have plenty. As for setting the gap, I've not done it. However, I think you rotate the engine until the tab is at the sensor to set or check the gap. If they need adjusting (in your case replacing), you loosen slightly the two mounting bolts, insert something of the correct thickness (feeler gauge or correct thickness of cardboard), push it lightly up against it, then tighten the bolts back up. Check again for follow-up (after tightening).