3-cylinder AZQ engine, leaky valves

The car is a 3-cylinder, 4-valve Polo with 105,000 km. It was parked overnight, and the next day it wouldn't start. The timing chain has jumped a tooth on the exhaust camshaft.

Removed the oil pan, removed the valve cover (the engineers really thought about the design of this engine). Adjusted the valve timing with the old chain. Measured compression: cylinders 1 and 2 at 13 bar, cylinder 3 at 10 bar. Then, I set each cylinder to top dead center (TDC) on the compression stroke and blew in 10 bar of compressed air. Cylinders 1 and 2 are sealed, cylinder 3 is leaking air out the exhaust.

Okay, I thought, well, the valve is just bent. I removed the cylinder head, took out the valves, and they're perfectly round when spun in the lathe. The valve seat from the third cylinder's valve is an "A" valve, which isn't okay.

"I lapped in the new A-valves, only on this seat, and it took me over an hour to get them to seal properly. Unfortunately, I don't have a valve seat grinder. I then installed the cylinder head, tightened the bolts to 30 Nm, and blew compressed air into it again. There are no more audible air leaks."

Okay, so now my actual question:
I'm familiar with the problem of burnt-out exhaust valves in the 3-valve engines, but not in the 4-valve engines. Although, in this case, the valve itself wasn't burnt out, but the valve seat was not in good condition.
Once, a VW trainer told me that this problem with the exhaust valve burning out only occurs in Austria, and specifically only in the areas east of Salzburg. He claimed that we supposedly get our fuel from Hungary, which is of lower quality. Everything west of Salzburg is supposed to get its fuel from Germany, which is supposedly of better quality.

Can you confirm that this problem does not exist in Germany?

Hello,

It seems that this engine occasionally suffers from issues such as broken timing chains and cracks in the valves.
I find it unlikely that the "brand" of gasoline is the cause, rather it's more likely a material defect.

Best regards, Rainer.

We have a fleet of Polo/Skoda cars (with 2 valves) here, and we've already had leaky exhaust valves in 5 of them. That's across the entire fleet of Polo/Skoda cars they have.

And all with mileage between 80,000 and 100,000 km.

The root cause is often the valve seat rings in the cylinder head itself!