NS1 had like 30% of German gas imports (Russia in total around 50%).

What German political decision back then do you mean that cut off supply via NS1?

If you take a look at ng prices you will see that the prices went up more than half a year before Russias invasion of Ukraine: https://www.macrotrends.net/3235/eu-natural-gas-prices The reason for this was because Gazprom stopped supplying the spot market and also bought storage capacity and kept it empty. All of that only made sense after the invasion to better blackmail Europe. It was their bad luck that China allowed them to attack only after the Olympics which took most of the force out of that blow. Anyway there was no sane way to continue this business relationship.

And then Russia refused to install the turbine, proving it was a ploy all along. Like the maintenance in the first place. Which is why they acquired gas storage in Germany, then ran it low timed with their illegal war of aggression. This is a theme of course; Russia invented another gas crisis every few years with Ukraine. It should have been a warning sign when they settled them by taking payment in the form of Soviet-era cruise missiles.

The gas was never cheap, either; apart from the money spent now to restrain the military buildup and invasion it financed, even at the height of supplies it was much higher price than China is paying, a price sustained by Russia using military force and more to restrain other (Asian) countries from supplying to Europe.

(This was obvious to everyone, right? A single majority supplier nation state charging a cheap price out of the kindness of their heart? No, of course not; neither cheap nor kind. It was a monopoly, built on blood.)

I don't think the turbine that was serviced in Canada was causal there. The turbine thing was earlier, as far as I recall it. Gazprom announced its decision in early Sep 2022, btw.