Let me guess without the picture. You said overflow. On the side where your right foot sits on the running board, look right at the center of the main frame casting in the center of the transmission section. If like my 2000 there is a ¼" pipe plug. Put a pan under the tractor and unscrew it.
If fluid comes gushing out, next check your hydraulic fluid sump.....it should be low. If both are true then your hydraulic lines that I assume run thru your tranny case, like my '63 2000 do, have a/some pin hole(s) allowing pressurized hydraulic fluid to be forced into the tranny case.
Mine had been doing it for years. Every once in a while I drain and add. I replace with new fluid since the stuff coming out is cleaning up the innerds of the tranny and is ugh looking.
Sound Guy put me onto this problem!!!!!!!!