Lately, I observed some strange when I try to start the diesel.

I turn the key to glow. After a few seconds after the light goes out, I turn the key further to try to start the car. Nothing happens. The starter motor won't turn.

If I turn the key back all the way to left and then try to start, it starts every time.

This does not happen all the time but is more frequent in the first start of the day, especially if I let it glow after the light goes out.

Is this an indication of a week starter motor?

TIA.