3rd transfer case seal in a year!

[smileynialley]

I have a recurring leak coming from the transfer case. The seal to the prop shaft at the rear is wearing away stupidly fast and causing transmission fluid to leak everywhere.
When I put my foot on the gas pedal, before the car moves i get a clunk. The same clunk happens when i sharply take my foot off the gas too.
Could this be linked with the seal leaking?
Any help would be great,
thanks