I wonder if there is a bit of gummy in one of those little piston that go in and out for the zz? Did you try the 'centering the needle adjustment' described in the service manual? It is the least invasive but intimidating the first time. Adjusting the needle bar would be after that - I had a bent needle bar in a 411G once - I was so frustrated with that machine until I swapped it out for a donor. I couldn't see any bend until I removed it. It didn't take long and it was easy to re-time. I'm hoping I can find the adjustment info to center the Singer I have. It is a bit newer but it skips like that, too. I will be flat out up to my eyeballs in paying work for the next 3 weeks so I don't know how much I'll get into my shop to play. GKs have a habit of showing up when I'm off. So we make mudpies.... Well some times I let them help me.
