Heinously late reply (mostly replying for future readers and for the thoughts below) but for the record, the bearings used are MR52ZZ (they're fairly generic, Takara used ones manufactured by NSK). The metal bearing is of basically the same dimensions, just solid metal (zinc alloy, presumably?)
As for legality (I'm not sure if NSK manufacture mr52zz's (edit: they seem to) any more but it's a fairly prescriptive spec, so they're likely all the same) I am generally unsure - it's an odd matter with toys this old. Most official bearings from back then are so old they would act much more differently to the original performance than fresh, aftermarket ones - but those aren't original parts. This is probably one of the earlier signs of the fact plastics is slowly becoming untenable. The future might be 3d printed (we're going to run out of base clips and dragon winders eventually), but that's not something the WBO can legally condone, I would imagine. Bearings though, are a much tamer matter.