type 1 rotary drive unit / service

Dear Sir, my rotary drive unit type 1 have given to me 15 years of troublefree service, but now, I feel that is a good idea do any inspection or change in it, could you be so kind to point which parts are a good idea to change in a preventive basis ? , if you highlight the parts in an exploded view layout will be very helpfull for me.
Thanks

Best regards

Renato Facchin