I haven't confirmed the make and model of transaxle, I just took your word for it. The VST/1800 is rather notorious in several ways, mostly relating to it being both very light duty, and not repairable, and it is therefore perhaps the worst one that you could turn out to have (though it could be completely satisfactory if it has been kept cool all of its life). That transmission does have a long series of letters and numbers stamped on it, and I think they are on the vertical rear face from memory, but they may be on the bottom. If you can post that long series, we can identify it. At that point it is relatively easy to discuss suitable lubricants.
