G6,Transmission axle sea

My transmission is leaking on my axle seal, i just took it to the mechanic shop, and they try to fix it, we buy a seal but it was too small and did not fit the transmission, but it fit perfect on the axle shaft, we went to buy another seal and it fits perfect on the transmission but was too big for the axle shaft causing it to leak oil. We try on all auto parts stores and could not find a seal that fits perfect on the transmission and axle shaft, do you think that the actual problen is the axle?? Maybe they put the the wrong axle in thats whay i could not find a seal that fits. Thank you

M