The friction disc just like the clutch pressure plates wear and distort with years of constant use and abuse (!).
If your machine has a clutch that is stiff to operate, has a wooden feel, or worse has started slipping and generally spoils your riding pleasure, perhaps an overhaul will sort out the problem. Specifying the clutch pressure Plate component at the same time is highly recommended.
Replacing ALL the friction discs and pressure plates is advisable - check the schematic for your model to make a more informed decision on what you need to order. Why not order all the gaskets you require at the same time - save money on shipping costs with a multiple order.