Keeping the lube level slightly below the fill hole seems to work well- - - -just leave it where a finger inserted into the hole in the side of the trans can reach the oil level easily, but it's not all the way up to the hole. Later-model transmission solved the problem with a lip seal, but it would require a different bearing retainer and input shaft to upgrade to the sealed model.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!