Goudrons: The axle cracked on the right side in the same area as the left side previously.
I suspected as much.
The hole must be there for a reason and you wouldn't expect that to be drainage. Perhaps it's there to help with a bit of flex in the axle and your rough track is over flexing it at those points.
As you've suffered repeated failures it very likely you're asking just too much of the standard Panda's suspension setup, but that shouldn't stop you Pandaing!
I wouldn't be comfortable welding it up to use or sell on.
You could replace it and keep your fingers crossed, but you've already tried that.
You could replace it and strengthen that one. Get someone to weld in a couple of strengthening strips above and below the holes that run past them by a fair way.
That will mess with the handling some, as you'll have taken out a fair chunk of flexibility between the rear wheels, then again the Trekking, 4x4 and City Cross all have thicker beams and handle reasonably well, but you might just find the next weak spot in the axle anyway.
Try and source an axle from a Trekking, 4x4 or City Cross and try fitting that.
Probably more of an option for the diyer.
Swap the car out for a Trekking, 4x4 or City Cross.
The Trekking was pretty rare as it wasn't in production very long and the City Cross is fairly new which tends to mean it'll still be quite expensive.
The 4x4's are now becoming more affordable and they are a bit of a mountain goat, They have their foibles but I never had any trouble with mine off road apart from the fairly low splitter under the front bumper. (Something they sorted on the Cross and City Cross)
I did used to hoon around in it off road when I went to some off road motorcycle events at the weekends. A couple of us with various 4x4's egged each other on with some mad challenges when we got bored on the bikes, apart from a knarly front bumper it went everywhere the others went and a few more places my old Discovery couldn't.
If you do decide to swap it out for something, make sure it's fit for the job.
There are plenty of jacked up hatchbacks that look like they could handle the rough stuff, but they are mainly standard under the rough looking body cladding.
The Dacia Duster is pretty well thought of, they were built for pretty shocking roads in the first place.
I'd give the Sandero Stepway a miss though, I had a petrol one a short while and it was a pretty scarring experience, though I'm told the diesel is a little better.