What are the early warning signs that indicates that your car's starter needs to be changed?

There don't tend to be warning signs. The starter either works of it doesn't.

thats common where we have a solenoid that has corrosion on assert contacts . if we have external ( not on starter ) solenoid .thats our suspect at first .but we may also have other issues.do check contacts .battery terminals etc for corrosion. looseness etc

if we keep getting odd slow cranking at first ( used to be called a lazy starter) we really ought to exchange to avoid issues. winter on way ..

The car will not start.

If your battery is 3 years old or older may be time to change out for a new one.

BATTERY low voltage

There are various signs. Slow uneven cranking can be the bendix drive, or weak battery. If the thing stops doing anything (solenoid problem) or just clicking. Most of the time you can revive a non-functioning starter by whacking it. But be careful you could break the case.

It sounds in your case like anything. Dirty connections, weak battery, maybe weak alternator. You can probably get all this adequately tested for nothing, if you take it to the right place. There is also sometimes a replaceable bearing the starter runs in, but more likely it is enclosed.

Who knows

I'd suspect the battery if it's the original. It can be tested. That starter should last another 5-10 years.

weak battery, corroded battery wires, but likely the starter has a bad spot... get it rebuilt instead of a reman unit...

Starters actually rarely fail. The problem is far more likely to be electrical, maybe battery, cables or connections.

More that likely it's the battery.