First Officer reported observing the engine number two torque rolling back from MTOP (Maximum Take Off Power) setting just after V1. The flight crew performed an air turn back and precautionary landing at the departure airport.

Narrative

Engine Failure.Captain (pilot flying (PF)) and I experienced a Number Two Engine Failure during takeoff. We were departing ZZZ Runway XX when just after V1 I observed Engine Number Two Torque was rolling back from MTOP (Maximum Take Off Power) setting. I called out the loss of power and immediately set RTOP (Reserve Take Off Power) on Engine Number One. Confirmed Auto Feather was active again and watched Number Two Engine stabilize at 2;200 pounds of torque. At this time we were switched to Approach and due to traffic on Tower I made the switch. Notifications to Approach were made stating call sign; losing Right Engine 'possible Engine Failure.' I was given a heading of 280 and nothing else. I repeated the heading and was met with negative results. I quickly switched to ZZZ Tower and advised engine failure as to now it rolled back to just 1;000 pounds of torque. ZZZ quickly canceled arriving and departing traffic and gave us vectoring and clearance to land. During this situation; the QRH was referenced and a decision was made to keep number two engine on due to the positive thrust it was maintaining. Fuel flow was normal; all appropriate gauges were in the normal range. No fire indications were also observed. While continuing back to ZZZ we also had left engine surges so this confirmed us keeping number two alive due to a possible double engine failure. Airport Rescue and Firefighting (ARFF) Crews were standing by at ZZZ. We landed safely and taxied to the cargo ramp with ARFF vehicles following. Upon mechanic's inspection they advised that the Number 1 Principal Injector was loose and damaged. Also advised they were changed recently but looked old. It should also be noted that the engine was cleaned (Routine Turbine Engine Wash) and they might have been left loose and not properly secured. The above statements were heard by several crews.