leaky seal again

[blumule]

my 3 speed trannys output shaft seal keeps leaking. this is the 3rd seal in a year. the seals are always name brand. ive also had a slight vibration at 45mph for awhile also but that appears to be in the frontend and not so much in the floor. Could these two be related? driveshaft was balanced last year but who knows if it was done right. i put a 1/4 ounce weight on the driveshaft in several places to to see if it made a change but could tell no difference.what do yall think?

[Art]

Does your transmission have a slip yoke at the back? If so, check the bushing that the yoke slips into. If loose, the seal won't last long and even a balanced driveshaft could vibrate.