2 weeks ago (at 120,000 miles), I had service done on the suspension -- new control arm, wheel bearing, and stabilizer bars/bushings. The mechanic recommended changing the differential fluid as well, front and rear, so we did that. After the car was done, it was stalling after start and at idle. Fixed that by disconnecting the battery for 10 minutes and having it 'relearn how to idle'. MPG on the highway had also dropped down to 28 from 33, but the car seemed to be running fine.
The other night, I'm driving 60 MPH on the Turnpike, I hear a PING, and the car starts skidding roughly, first for 1 second, then 2 seconds, then 4 seconds, and it comes to a complete stop. I couldn't turn the vehicle to the shoulder and after stopped, couldn't move it whatsoever. Hazards on, left the vehicle, called 911, and tried to warn other motorists with a flash light. Eventually the police came and they had to ram the car over to the shoulder as the front wheels had locked up. Had it towed to a nearby shop and spent the entire night in the boonies.
Right away, I suspect the differential service but there was no noise before the seizure. Found one of the only similar cases here on SubaruForester.org (can't link). In the morning, the shop diagnoses the car; "Found front differential locked up and had no fluid. Ring and pinions damaged". The mechanic also told me there was no fluid sprayed underneath. He wanted $7000 to install a new dealer transmission and transfer case, but told me flatly that it's not worth it and I should tow it back to the original mechanic who most likely made a mistake.
The vehicle has been driven 1500 miles since the differential service 2 weeks ago. I doubt the differential lasted that long dry (?), so it must've been a leak. How could this have happened during the service? Should I expect the mechanic to fix it... should I get a lawyer?