P0302 cylinder two misfire

One guy said me it can be a vacuum leak even at the intake manifold's gaskets, the rubber sealings can be already worn, since its a 16 years old car. And also that might be why after the change of the O2 sensor its worse now, because now its monitoring properly, and now like every second its a sputter on the exhaust, while its been like 3-4-5 seconds with the old O2 sensor.

I've been searching for a picture of an AZD engine Golf 4 (thats not mine, but im not at home, cant make a picture of it), and I'd ask again, which hose should I blow with smoke. Atleast I want to try with cigar/vape, I know its not so exact by that, but worth a try.

Thank you, I'm not home and im not with this car now, and I'm going home only next Thursday, so I can check only then. Also as i've said, its not a picture of MY engine, and the brake booster hose is which i've replaced already.