RIDB-1c-1982-01R (Ld)(Cu)

Should not be Zinc Rot on that coin if attributed correctly which it is, That Ridb is on a copper composition coin. hence the (Cu) in the attribution:
RIDB-1c-1982-01R (LD)(Cu)

You've got some slight verdigris going on around the lettering and devices, and you should take care of that it doesn't get better with time. 100% pure acetone, maybe 20 minutes to loosen the crud up, remove, give it another go with clean 100% acetone, just a short dip to take off any fouled acetone from the previous soak and see if that helped it. don't leave it in the acetone for a long period, don't use tap water, the chlorine is bad.

it's been circulated, you could probably spot treat it with some q-tips and pure acetone and roll the q-tips over the surface to pick up the grime after a 20 minute soak without lowering it to a lower circulated grade than it is really, no scrubbing though.