Wow, been off here for a few weeks just logged in and read a bit of this.
Nearly the exact same thing happened on my 4200 about a month ago - luckily I was pulling out driveway when it happened, if I was driving would of been in a ditch and total write off, on motorway I'd be dead quite frankly.
Basically the lower arm on front drivers side collapsed and kind of pulled through the hub at same time, so wheel buckled in at about 90 degrees, was just a loud bang and felt the front end go funny as I was reversing out my house.
Had to get a couple mates round to help get it kind of back together as driveway was blocked off, then we got it across to mechanics on back of recovery truck. New lower arm, upper arm joint, various washers and a used replacement hub, with labour just over 2k - main thing is I didn't die this time I guess.
She's gone into winter storage now anyway so whilst there she's being gone right over by a mechanic I use before being MOT'd in February, God only knows what shape the rest of the suspension is in - she was knocking a little and we were already going through replacing bushes etc but after this we've agreed she's going to be gone over a lot more thoroughly.
Knocked my confidence in her a bit now, will be a long while before I go quick in it again..