Bad day today I had my 01 400 explorer up on rear jackstands while running to check for a bent rear wheel. It was in two drive mode blipped the throttle and bang! awful noise occurred. I took it off the stand and no 4 wheel drive look at the intermediate drive shaft not turning! Now I see a puddle of oil under the countershaft sprocket. The trans case is cracked in front of the sprocket. I'm now studying the service manual and I see two chains inside the cases I'm thinking one must have broke and broke the case. Is this common?