'78 vw

I know old VWs have personalities…mine loves to refuse to start after doing errands. Four stops, OK. Fifth stop, it refuses to kick over. My mecahnic cannot figure it out. I have to sit patiently for about a half hour before it decides to start. Any ideas???

One possibility is a “heat-soaked” starter.
On some cars, there is a need for some insulation between the starter and the nearby exhaust manifold in order to prevent this from happening.

That would be my guess. Starter gets too hot.

It would help to know what type of VW you’re talking about.
Rabbit, Type 2 Bus, Beetle, or what?

Each have their own quirks if by not kicking over you mean the starter motor does not physically crank the engine over.

Start parking on a hill and catch the car in gear. This will confirm the “heat soak” of the starter others have mentioned. If it starts via compression (catching it in gear), get some insulation around the starter to keep it cooler. Rocketman

Heat soak was never a big problem on this era of VW.
On the Beetles and Type 2 Bus, starter problems (depending on the exact symptom which is still unknown) it was usually a worn transaxle starter armature support bushing or a faulty ignition switch. The worn bushing usually meant a new starter.

On the Rabbits, etc. (again, depending on the symptom) it could be a worn starter, faulty ignition switch, faulty neutral switch (hardly ever a problem), or a fuse block problem (common).

Odds are the starter is just flat worn out and no matter which model of VW it is, a starter problem on these vehicles is very simple to diagnose. No idea why the mechanic can’t figure this one out.
Put an inductive ammeter on the starter and see how much current it’s drawing. If it’s pulling a steady 200 amps or whatever after the initial current surge the starter is going; and will eventually be gone.