Why are lift arm bolts elongating the hole in the shell?

[ShrimpBurrito]

Just notice this the other day, so I'm pretty sure this hasn't been like that for awhile. The bolt that holds the lift arm into the shell (torx head on the outside, acorn nut on the inside) seems to be elongating the hole it's in. I don't know if this is purely cosmetic, or if it's a structural problem I need to address. Presumably, there is too much tension on it, but I'm not sure where that might be coming from.

Has anyone had this happen before? Any thoughts?

Pictures are attached. Please excuse the grime -- it needs a cleaning.

Thanks,
Dave