IF it's due to a wear groove in very old/ hi-mi trans , and you are able to "locate" the new seal NOT all the way in the same depth. Like some seals are 3/8 " (10mm) deep , the sealing lip can be contacting a fresh point on the output shaft ?? And it would be "outboard" of the grooved portion , you know.
Other reason excessive bearing/bushing play or vibes from unbalance/ resonant - impacting seal lip ?
Possible remedial approach, especially if your install is to blame - goto a shop where a good written warrant ylike 12k+ mi and 2yr + , where if you find a driveline specialist to do this , they either point out the "culpret" OR you have them redo the leak under warranty. All the while you decide under that extended time what to do with the car.