Drivetrain Problem Diagnosis - 2003 Focus

2003 Focus 2.3L PZEV MTX 75 5 speed transaxle 160K miles
Inherited it from my son with what I think is a broken transaxle.
A couple months ago I took it for a drive because he said it developed a
bad vibration in the drive train and wanted my opinion. There was no vibration at all the first time up through the gears but after turning around and heading back after getting some heat into it it indeed did vibrate only under acceleration. At light throttle and engine load on level road the vibration was barely noticeable.
Had it towed home where we put it up on jack stands and checked the motor mounts, CV shafts and anything else that could have come loose on the chassis and found nothing.
Took it for another test drive and again when cold no vibration could be felt. Upon making a turn then getting back on the throttle, something popped (my sons description) and the car would no longer move under it's own power. Pushed it back into the garage, applied the e-brake, put it gear and released clutch, and nothing. It wasn't going nowhere.
Now a couple months later, this weekend while running the engine I, for the hell of it, put it gear and released the clutch while expecting nothing and rolling under its own power it went.
I've replaced transmissions and clutches on rear wheel drive cars but don't have any experience, yet, with front wheel drives. Does anyone have any idea could be wrong with it seems like the transaxle based on my description? It's be nice to know what I'm looking for before I start wrenching. :)
Black Dragon

I'll show you MY telex number if you show me YOURS ...
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