is my motor any good?

I used 2 work 4 a water weller and he could check pump motor condition by checking resistance in his running and starting windings and refering to his chart to see if the readings were within limits. where would I find a chart of limits for a motor that I bought at Princess Auto where they really couldn't tell me anything about the motor in the first place. how can I tell if this motor is wore out? It's a 24 volt reversible motor but I've been running it with a 15watt solar panel 2 run a solar tracker. so it sits all day having partial volts pushed at it untill the sun hits it directly, it tracks for a minute or so, turns away from the sun alittle, then has partial volts pushed at it again til the next time. Now this winter it seems weak. It worked better last winter. I remember hearing years before that amps = heat and when motors run at low volts, amps and heat rise causing longevity issues. How do I find out, Is my motor weak?

have you checked the motors performance with a full 24v supply? you said it sits all day with partial volts, does the motor run with the partial volts or does it just dissipate the lower supply as heat? am a little confused. Karl