Thorens TD145

I have a Shure V15 that now plays only 1 channel of a stereo LP, so I'm guessing that the cartridge is failing. Checked and moved all connections to confirm that the problem is not associated with the tuner or speaker connections. If this is a symptom of a failed cartridge, what are some newer cartridge options? I'm considering a Shure M97? But will it fit, etc.

I have a TD145 MKii with Grado gold. It works pretty good. But if I were you I would just replace the stylus. Type III would outperform Grado gold.
The Audio Technica AT440mla has a nice synergy with the Thorens arm. Give it 20-30 hours break-in time and you will be incredibly pleased.

When you say, "Checked all connections...", did you renew the connections where the tonearm wiring plugs into the back of the cartridge? I have had a similar problem with an M91 which started working again when I unplugged/plugged in the connections.
Yes I have reconnected all connections to the cartridge at the tone arm head. Haven't been inside of the turntable to evaluate the wiring as it leaves the tone arm though.

A common problem with these old Thorens tables is the internal wiring could be frayed or totally broken off all the way back to the Arm connection..I had the same problem with my old TD 160 and found the left channel had a disconnected wire at the terminal junction..Once I resoldered the problem went away..Its still possible the cartridge is bad but don't rule out internal interconnect failure........
It's pretty easy to test if the cartridge is failing. Change the connections at the cartridge while leaving the turntable rca's plugged into their current location. With the phono preamp turned off, of course, swap the red and white leads and then swap the blue and green leads. This swaps the left and right channel of the cartridge.

If the same speaker has sound as before the swap, then the cartridge is OK and the fault lies with the tonearm cabling. If the sound now comes from the other speaker, then the cartridge is the culprit.

If it is the cartridge, you won't be able to fix it with a new stylus, you will need a whole new cartridge.