You can't change the synchro ring without opening the case.
I had problem similar on my old 550, sometimes 3rd gear grind during 4-3 step, I had removed gearbox and revised by myself, I changed synchronizer rings (zf type) of 3 & 4 and replaced fork for 3-4 gears because consumed.
For me you must open gear box and:
1- check syncronized rings
2- check the syncro teeth consumation in the gear
3- check the syncro teeth consumation in the hub shift ring
4- check the gap between fork and hub shift ring.
5- at assembly verify and eventually adjust the lever gear with the gear shift shaft on gearbox.
Apparently the syncronized system of daytona are very similar to that alfa romeo giulia, (elastic ring), different to the ZF type based on bronze cone ring.
Pictures attached are of giulia and drw is of Daytona.
If points 2-3&4 are consumed can be reject the gear also if the lever arm is correctly aligned, because the teeth work in a conical portion and not in cilindrical portion.
If points 1&4 are consumed can be a low syncronization torque and consequently grind.
In a transaxle gear system the synchronizer rings have strong work because during the synchronization phase they must to win the an moment of inertia bigger than an gearbox directly coupled with the engine, the increasing is due to the inertia of transaxle shaft.
Last generation of gearbox are fitted of multicone synchronizer that multiply the torque and reduce the shift force.
For example, F 550 have double cone on 1-2 and single cone for others and it only with lever hand but 575 have 3 cone in 1-2 and double for others in order to have a sure synchronization with the F1 system, that not permits fault shift.
Sure your mechanic will be more expert than me.
I am waiting for your developments ....