Something which I observe on virtually every RTR model with plastic buffers is a horizontal mould line crossing the buffer face:
This is an example of the problem on a locomotive, but it a very widespread issue on all rolling stock, particularly wagons with a one-piece chassis moulding.
To fix the problem, I use the same solution on all of my rolling stock which exhibits the problem.
I use a relatively wide file (shown in the pictures below) to remove the mould mark from the buffer face. The reason I use a wide file is to prevent accidental slippage while filing and to ease the process of filing the face to a curved shape.
I then paint the buffer face and apply some weathering powders to similate the 'touch point'. Problem solved:
Graham Plowman (11/09/2021)