ALH TDI Water Pump Leak?

Hello everyone,

In my project car, I've installed an ALH engine from a Golf 4, which I've converted to use mechanical ESP (from a Land Rover Defender) / M-TDI components.
A few days ago, I wanted to see how fast the car could go. The ESP system allows the engine to rev quite freely. I don't have an exact tachometer, but I think I had it above 5,000 RPM for a full minute. Yes, I know, not very fuel-efficient...

A little later, the water level warning light came on. The expansion tank was empty. The coolant was leaking from the right side (belt side) at the bottom of the engine block.
While I couldn't pinpoint the exact location, I can't imagine any other damage besides a leaking water pump.

Over the next 50 kilometers, I consumed approximately 2.5 liters of water.

Two days later, I drove my car 20km to my mechanic's shop, and strangely enough, there was no more water leakage. Now, I can't even determine the exact location of the leak so that I can fix it.

Can anyone make sense of that?

Thank you in advance and best regards.