Hey there, the starter on the L230 skid steer can be a bit tricky to reach. The best way is usually from the bottom, removing the skid plate to give yourself some room. You might also need to loosen the hydraulic lines for better access.
It sounds like there might be a hydraulic issue, especially if you're seeing weaker performance and trouble with the left track motor. I'd recommend checking the hydraulic pressure, particularly in the control block and valves related to the left track. That flopping left handle might indicate...
That metallic knocking noise and shaking usually point to an issue with motor mounts, bearings, or even a connecting rod. It might be best to check these areas and, if you're not comfortable with it, consult a professional.