Lstamp

I took my 2000 Forester with 130,000 to a brand new Subaru dealer to have the Oil changed. After it was done, I drove my Forester down some snow covered roads, pressed the gas to get some wheel slip for fun. I got some slip, then Bang, shudder. Something shifted hard and the wheel slip stopped. I repeated the process. It did it again. The bang was hard as if i had driven over and hit a big rock underneath the car. I noticed a earlier post that an oil change crew had replace the tranny fluid with oil in error. Would that have accounted for my event. How can I tell if that happened. Oil vs Tranny fluid. Smell, look taste different? I have driven about 50 miles since the change. Lew