Just like the friction disc, the Clutch plates wear and distort with years of constant use and abuse (!). So if your beloved classic has a Clutch that is stiff to operate, has a wooden feel, and generally spoils your riding pleasure, perhaps an overhaul will sort out the problem.
Take a look at the online catalogue for your model, this will help you put together your 'shopping list' of all the items you will need, including plates, friction discs, Clutch springs, gaskets and seals, maybe even a new cable to ensure smooth operation.