I bought a road bike that was claimed to have 2300 but when I got it the rear derailleur was Claris out of the box but the brifters were 2300. You can buy a Shimano road rear derailleur from 6 speed to 10 speed that has a 1.7 movement ratio so you could if you wanted use a Sora, Tiagra or even 10 speed 105 rear derailleur. The pull ratio in the brifters may be different but the actual movement of the rear derailleur is all set at 1.7.
Might be worth removing and checking the current derailleur and perhaps checking it can't be repaired but considering I think they stopped selling them officially in 2013 in could be quite old and well worn. Although I'm sure pockets of old stock seems to often survive sometimes 3 years or more after that.