Hi Mike, it's not just you who has the no.8 problems. A few years ago no.8 shot were all lead, slightly misshapen and soft, closed easily and gripped. When your tub got older, the grey shot oxidised and became greyish white. When you put them on, they stayed put.
Most no.8's that I've seen lately are hard, black, perfectly spherical, don't oxidise and appear to be some much harder compound. You can squeeze them on and find they're gone next time you look to check why your float isn't shotted properly. I've stopped buying them.
Like others, I've gone over to using Stotz or similar in no.8, 10, 12.
These are like tiny sections of lead wire cut along the side and fixed on the line with a tool sold with them. They stay on, even on thickish line, and what's more they slide easily, allowing you to move them around to change your presentation without damaging your line.
I got interrupted between writing and sending, so you've probably read all this by now from OP's.