When the rotor blades edges are not anymore coated , it can have 2 rootcauses ( at least ) :
mechanical contact between the 2 rotor blades : origin is often a play on the rotors shafts ( brearings must be replaced ) .
or poor air filtration : small particles go thru the air filter and are sucked inside the S/C . They destroy the coating ( teflon or ceramic ) on the tip of the rotors blades . It is not so critical as the play on the rotor shafts .
On both cases , there is a ( slight ) lost of engine power due to the pressure "leaks " inside the S/C in those areas.
Recoating of the blades is possible ( call "Jon Bond Performance" in USA for instance ) - approx 200 USD if I remember well . But if the origin of the issue is not fixed ( bearings aeging for instance ) it will happen again ... and again .
Would be good to check by yourself the rotors shaft play . If not possible ( remote purchase on internet ) , be ready to spend money in this S/C refurbishement.