RB300 maintainance...

I noticed that on the most inner grooves especially on the extra long-playing records where the grooves come as close as possible to the record label that the sound greatly degrades and becomes too mushy and undetailed. It happens approximately 1.6" apart from record label. Before that the degradation seems to be unaudiable. The very beginning of the playable surface seems to be even too bright, but that's I believe an issue of a load impedance and can be easily resolved.
I checked the cartridge allignement and it seems to be at its maximum precision.
I assume that tonearm moves heavier towards the inner grooves and needs some attention.
Please help me out. My analogue setup is J.A.Michell GyroSE/Incognito-RB300/Lyra Helikon(Benz M.09 as backing up)

THANKS!