I've never leased a vehicle but I would think that it would be a reasonable expectation that if something broke on the vehicle that you leased, you would be obligated to have it replaced.

Idealy if you lease a new vehicle most all parts are covered under the factory warranty, so the factory pays. The problem occurs when the warranty runs out or does not cover the part. I would say yes, you are obligated to pay or replace it with a comparable part.