Is this a common repair? I replaced this at 56000 miles, again at 70,000 and now it's leaking again at 86000 miles.
Rear Output Shaft Seal on 1999 Chevrolet Blazer
Even if this was common, it shouldn't be re-occurring every 15,000 miles. There may be a worn out bearing or bushing that is causing the seal to go bad. Have the shop check for excessive lateral movement in the output shaft (which will cause failure of the seal)