In English, we would probably say this in one of the past tenses. "The team has been in the lead for months". Not sure if this is another duo-ism to make it present tense instead. How would it be commonly said in German?
In German you would normally say "Die Mannschaft führt seit Monaten" (The team has been leading(/in the lead) for months). Die Mannschaft führt Monate lang sounds artificial. There are few situations in which this could make sense, for example a hypothetical, finite period of time that could be in the present, before or after. Usually I would say "Die Mannschaft führte Monate lang" in a past tense, referring to a team that had been leading for months, but fell back after this period. But also here "Die Mannschaft hatte seit Monaten geführt" is much more common, so the Duo phrase is somewhat abstract.....
The scenario I imagine this phrase making sense is one of speculation. "The team is leading for months, then they decide to trade their goalie. What would happen then?"
"the team leads for months on end" This accentuates the continuity of the leading.