[Guest]

If enough of the coil has survived the corrosion, then
use a pin or needle to count the turns. Place the point
of the needle on the former, and using very gentle pressure,
slide it along the coil, counting the "bumps". Trying to unwind
the coil and count that way is doomed to fail. After you have
the number of turns, make a careful drawing of the coil,
including the number of turns, direction of winding, length
of the coils, and distances between the sections, if any.
Then carefully unwind the wire, and try to compute a diameter
of the wire. The exact diameter is not terribly important. Anyway,
from the length of the coil, and the number of turns, you
can get a diameter for the wire. Try to get something reasonably
close in diameter, and rewind.

Good luck