Hi from what I remember reading on the earlier models like yours the drain from the windscreen scuttle was not long enough & dumped the water onto the top of the gearbox. The water then collected between the gearbox casing webs in the valleys & this is where the levers for the gearchange enter the gearbox.
As oil seals are designed to keep the oil in the transmission not water out the water eventually found its way past the seals & into the transmission. I believe that extending the scuttle drain pipe further & away from the transmission top & to the rear of the vehicle as in the 244 models cured the problem.
