Is there any way to tell for certain if the wooden casters are original?
ehc68, wood casters were notorious for "wearing out" quite quickly because of the abrasive action of rolling the piece of furniture around on the floor. Both, #1, the surface that touched the floor and #2, the center hole through the wheel because the weight of the furniture would compress the wood unevenly and/or "out-of-round" because of the grain of the wood, which would then cause the wheel to wear even faster.
Dual wheel casters were probably used to retard and/or prevent the #2 problem but I don't think it would completely eliminate the problem. A metal insert (bearing) in the wheel's center hole would be the only preventive measure.
So, what I'm saying is, check the caster wheels for any "wear".