I wouldn't be so sure it has completely failed although it is definitely past it's best. Like I said, mine took 2 minutes with no obvious signs of damage to the drive train, and I've never heard of a VCU damaging a subframe.
I hadn't heard of it until i found the problem either.
It's surprisingly common. Land rover issued a bulletin over it. There are quite a few people reporting it to be tied in with VCU failure. Apparently the position of the diff in the subframe means more force goes to the off side front mount point of the subframe under heavy load. This pulls a captive nut through the chassis leg causing a split, thus creak and knock that leads to increased failure rates of the diff mounts. I'll post the bulletin at the bottom because it seems to embed.
A stiff vcu would also cause strain on the drivetrain, which would strain the subframe in the exact same way (as seemingly many people are claiming online). If 45s and under is a new/good VCU, i'm 14s slower at a 59s average. That's not really a small amount for something that is supposed to be precise. It was not smooth motion at first so it will probably spike, plus, my freebie is a bit more abused than some (which will have contributed).
I think the thing to take from this is that mine failed early on in the 'seizing process', in part due to hard use, but had the vcu not have been at fault, it probably wouldn't have happened at all. Why am i so sure? Mine is a facelift td4, which (i have just learned) has a reinforced chassis member on the OSF mount, designed to combat this 'design' problem, yet mine still broke. There must be quite a bit of strain involved to crack the reinforced version... In hindsight i am certain that i was kidding myself by passing it all off as coincidence and hoping for the best.
I guess i could be wrong, but i suspect you are fine because all else is solid on the car, so there are no weak points yet. Personally though, if my results where 2 minutes and i was getting a stiff full lock [with the luck i have] i wouldn't be sitting around. For the price of genuine diff mounts/seals [fitted] and a subframe repair it is actually cheaper to buy a GKN vcu and genuine carrier bearings (which is also an easy job to diy). I was only really hesitating on a new vcu because of the ridiculous amount of money i have already had to spend on the motor.