Engine.
At a bare minimum, a valve check at a reasonable interval ... say 1000 miles, maybe?
That is assuming there are no odd noises, shifts smooth and the clutch operates smooth.
Here is the oiling system.
View attachment 227588
If you follow the oil stream, flow from the pump goes to the trans and to the motor via two separate channels.
The flow to the motor splits immediately post filter ... one side to the crankshaft and the other to the valve train.
The valve train will starve first because of the location and channel length. without oil, it would be clacking, ticking and banging.
If there is no unusual wear on the cams and valve train, it's probably not an issue.