RB300 maintainance...

Now we knew the problem didn't caused by the cartridges.
I don't think the problem is relating to the anti-skate, cable or anything.
I'm sure the problem is caused by the misalignment of the cartridge or even the arm was mounted incorrectly(I mean the position) or both.
Does this problem happens to one particular record or it happens to all your records?
Try to put the cartridge at the end of the record. Is the cartridge parallel to the groove? Now try to put the cartridge at the beginning of the record. Is it parallel to the groove again? For a properly align cartridge, the cartridge is always parallel to the inner edge(the end) and the outer edge(the beginning) of the groove.

As I sugguested before, you need a Denessen Cartridge protractor to properly align the cartridge and arm.

Make the following arm test:

Place the stylus guard in place, and put the arm in perfect balance at zero grams, the anti-skating at zero too. Then slighly tap with your finger the arm to slide it towards the spindle and to the back, to rest position. The arm should be travel free as a feather. If you noted hesitation or any anomalies, unfortunally the bearings were damaged in a degree accordingly to the anomallly.

I hope this is not your case, because there no more could be done to fix it, only the manufacturer.

Listen to cds or just the middle of lps. Another reason to hail the lps as the "superior medium", I guess. BTW, is it "analog" qua analog that sounds better or the lp storage/retrieval medium itself? Put another way: has anyone (aside from people in the biz which don't seem to bother with Agon and such) ever heard analog master tapes to determine whether the lack of impact noise lets the touted analog liquidity shine through? Insofar as your problem goes: once properly set-up, any tonearm describing an arc can only be optimized at two points on the record, the tracking error will always be greater towards the inner grooves. That's life I guess, although I am sure some wise guy/gal out there will have some new audio-gibberish explanation to set up the arm voodoo tweaking so that the laws of physics (and geometry in this instance) cease to apply and that their golden ear has assured them that they are on to something that no one, hitherto, believed possible. People have tried radial tracking arms to avoid this problem, causing other gremlins I understand,. The other solution is the use of a longer, or broadcast-type tonearm; these have not caught on have they. Like I said, tonearms can only do so much. Don't try to transcend the limits of those things, you'll only end-up feeling dejected and sad.

I've used protractor that alignes the cartridge to the middle grove and to the edge groove.
What is the price of Denessen Cartridge Protractor?
Now I'm staying tuned to check the bearings.