These days, engine manufacturers are not any more in the business of selling engines, but selling thrust.
Rolls-Royce were the first to offer this, and today most Rolls-Royce engines send telemetry data to four centers, the biggest one in Derby, in Great Britain, where every engine is under surveillance. An inspection can be scheduled at or spare parts can be directed to the right destination even before the pilots or the airline know that one of their engines has a problem.
By now, 80% of Rolls-Royce engines are sold at a loss which is recouped by a hourly fee paid under the TotalCare (.pdf!) program, and that center in Derby is monitoring maybe 4000 of them at the same time. Rolls-Royce has accumulated a treasure of engine operations data, which enables it to consult airlines on best practices. This makes it very hard for a third party to steal maintenance business from Rolls-Royce. All maintenance cost is covered by the TotalCare fee which now accounts for more than half of Rolls-Royce's revenue.
GE and Pratt&Whitney have similar programs. In GE's case, it is called OnPoint, sold as "Power by the Hour". The airline does not pay for the engines, but for the time they are flying. Now the engine manufacturer has a strong incentive to improve the reliability of its engines, but also a strong lever to push out third-party maintenance providers.