In NYC, it's common for cranes to be rented for construction work - the company that owns the crane is responsible for maintenance etc. However, the crane worker's union requires that the contractor performing the building work hire a master mechanic, as well as oilers (no, really) for the crane, as well as the actual crane operator who sits in the cabin and does the work.

Usually, these people are not permitted by the crane owner actually to perform any work on the crane at all.

By the way, salary for a master mechanic in NYC is around $150,000 p/a.