It's surprising what abuse stoves go through, ending up with damage like yours. In theory, a collapsible 1-pinter is easy to take apart with the included spanner, used on the riser hexagon. Only the riser to tank seal gets any wear. But try to dismantle by the burner hex, and the burner washers may end up disturbed or even cracking. Or even worse, lose the spanner and tighten/loosen the burner with a pan leg shoved between the burner tubes.
Quick update… the fettlebox seals kit arrived today and after some careful straightening of the cup I’ve fitted the seals and tightened everything up. Not a blow to be seen and she boiled a kettle in no time flat… as @Blackdog says, a little powerhouse and pretty good value for £10. I can see her and my Optimus 48 being the go to camping stoves
Good work, glad you got it up and running. There's generally a reason if these old brass stoves aren't performing and putting a smile on your face, it's just a case of tracking it down.