Help, my TDI won't start

Hello, can anyone give me a tip?
I have a Golf 4, manufactured in 1998, with a 110 horsepower TDI engine (72,000 km).
Problem: Basically, the engine needs several...
Revolutions to start. It's been like that from the beginning.
It starts up quickly.
It starts up cold.
If he hasn't started yet, I'll start him right away.
start again or drive only a few hundred meters and...
Turn it off.
It won't start again!
When you turn the ignition key, the starter motor engages.
The engine starts to fire, it sputters a few times.
And then it's silent again, and the starter motor continues to run. And again and again.
After a few days of rest, it might start up again with a bit of luck.

I had the car checked at VW, and they initially replaced the voltage relay.
replaced with a new one for the ignition.
Error reappeared.
Then it was the starter's turn, and it needed to be replaced.
Error reappeared.
No error codes found in the diagnostic memory. VW workshop doesn't know what to do.

Has anyone ever experienced something like this before, or can anyone offer me some advice?

Thank you in advance.