Replacing tonearm cable - Dual 604

I gave my son his grandfather’s old Dual 604 turntable. But there’s a short (hum) in one of the channels. I’m not sure where the short is (it changes sides when I swap the connections on the back of his receiver). I suppose it could be in the cartridge which is also at least 40 years old. It works for a while then the short appears. I’m thinking of replacing the tonearm cable first but am wondering if this is doable on this table given the construction. I’m not sure the tonearm can be easily removed but I’m handy and there’s not much to lose at this point.

Anyone have thoughts on this? I haven’t gotten into it yet but it doesn’t look nearly as simple as on my Clearaudio Innovation table. 

Other things I should try first? 

TIA

mgrif104