Not something I readily admit to, but I had a similar situation and ended up drilling a hole in the lower end of the motor case (missing all windings and other internal parts) so any fluid getting in the motor would drain out the bottom.
In this installation to prevent the leaking fluid from spraying all over the unit I would add a drain tube.
Another thought is to add an oil slinger on the motor shaft that would send any fluid out the slots in the coupling housing. Plus that would give the operator a chance to see the fluid before it collects in the motor, especially if he has to mop it up more than once.
Are you sure it is something leaking into the motor, or is it condensation forming inside of the motor when you turn it off? You mention butter, so I assume this is a food production area, probably kept cold. When the motor has been running and warm, then you shut down in a cold moist area, as the motor temperature passes through the dew point, condensation will form inside and eventually, the winding insulation will absorb it.
The solution is to not allow the motor to get that cool, keep it warm at above the dew point of your facility (dew points vary by humidity). Some VFDs offer the ability to trickle low voltage DC into one winding as a motor winding heater. If yours does not offer that, you can use heating bands around the motor and a separate circuit to power it whenever the VFD is not running the motor, or use motors that have winding heaters built into them.
I like it. Similar to a drip “skirt” on HV terminations. In fact they make those in heat shrink material, that might be a good way to implement it if you could find one that would shrink down to the motor shaft size.If you really have a problem with a liquid running down the motor shaft and passing through the motor seal and bearing. Something I saw many years ago when I first started in the trade may help.
The old timers . the old timers press mounted a slinger collar between the motor bearing , seal and the coupler. Just a simple disk that is large enough so any liquid that would travel down the shaft redirected to the outer edge of the motor housing. Any liquid that would migrate down the shaft while the motors is running would be thrown clear of the motor. It can get to be a bit messy around the motor while it’s running.
I have not seen anybody use them recently. I guess that the seals n the older motors weren’t as good as they are today. A good machine shop should be able to fix you up with one for your motor