Manual transaxles are 100% mechanical and do not have a pump, and their proper function does not rely on anything hydraulic. They are assembled per factory specifications—no oil is ever put in them prior to shipping, which means they will arrive perfectly dry.
Automatic transaxles are a competely different story, as they are much more complicated. They have a hydraulic section (transmission) at one end, a mechanical section (differential) in the middle, and another hydraulic component (torque converter) at the other end. There is no way to ensure that an automatic tranny will work properly (and not leak) without testing; thus, all GoWesty automatic transaxles are filled to capacity in both the differential section and AT section, and then they are thoroughly tested on a transaxle dynamometer. This is how we know that they are 100% perfect before they ship out. Once the testing is done, we do the following: Vanagon ATs are drained of fluid (except for diff fluid, which is topped off); Eurovan ATs are shipped full of fluid. At the time of installation, when the external oil cooler kit is fitted, it will be necessary to add another pint or two to compensate for the ATF that will fill up the external cooler, thermostat, and hoses. This should be done after the transaxle is thoroughly up to temperature.