Heat causing resistance to Starter

[Sixt8Chrgr]

As what I stated above, I think that when my 69 RT 440 gets hot either the starter is failing or resistance is building inside the starter or resistance is building somewhere else, I THINK!
So the symptoms are: when the car gets hot, sits for less than 30 minutes, turn the key the starter acts like the battery is dead with the VR or solenoid making the buzzing noise. Or the starter just clicks. I keep turning the key and if finally starts. Maybe the starter heat soaking?

One other disclosure. When the car sits for a while it takes a while to start. So the starter has been exercised and has a little age on it.
Any ideas guys!

Thanks