Lifter falling apart?

[Rat72]

I've been having vacuum issues so I thought I'd adjust the valves. One of the lifters was really spongy at zero lash. I've seen this before where the lifter just loses it's oil pressure so all that is providing pressure is the spring. But something was strange, at zero lash the rocker arm was about 1/8 of an inch higher on the stud than all the other rockers. And the other rockers were almost exactly the same heighth on the stud as each other. I'm wondering if the c-clip in the lifter broke or came out somehow? Has anyone ever seen this happen?

And if it did happen, I would guess that I'm getting very little lift out the valve (intake) or possibly more lift. Could this cause the low vacuum problem I am having?

Thanks,
Whit