Tonearm issue

That would be like attacking a mosquito with a shotgun. You may accidentally kill the mosquito but you’re also likely to do other damage. If you really think you’ve isolated the two possible causes, which we cannot be sure because you haven’t told us how you eliminated all those other possibilities, then I suggest you concentrate your attention on the white/blue leads and the RCA plug. Can you think of any reason why either may have gone open circuit? One place where tonearm wiring sometimes fails is at the pivot, where the 4 tiny wires have to make a right angle turn. Long term use of the tonearm can wear out the insulation at that acute bend.

Did you check the cartridge? I have never had the tonearm wiring fail.

OP, I had the same issue w/ my Technoarm, left channel would go out intermittently. The tonearm cable was frayed at the RCA connector, apparently this is not an uncommon problem w/ the Technoarm.

I upgraded to a SME M2 9R, however, I do intend to get the Technoarm fixed eventually. When I do, I’ll send it out to a professional to rewire.