MGB starting when warm issue

[MSHolme13]

1978 MGB GT. When cold spins over and starts OK, but as soon as the engine is warm and you turn it off, the engine barely turns on the starter. Battery is new (and turns OK when cold) but as soon as it's warm it's like the battery is depleted.

If I let it cool down it spins over fine again and will re-start.

Any ideas? Starter motor?

[MSHolme13]

It's strange becuase the starter is engaging but just not able to turn over the engine very fast. It does just turn over and is often enough to start it.
Battery and alternator are fine and later/next day there's plenty of power in the battery to start it again.

It's almost like there's drag on the flywheel preventing the engine from turning over. I don't think it's electrical.

Strange......