Mark, because the base is much thicker than the aluminium patch you have used, and the pop rivets do not provide a very rigid joint, the cracked base will still be carrying part of the load despite the patch, and the crack will therefore continue to propagate. Even if you were able to make the patch and joints much more rigid, the sharp end of the crack creates such a profound stress concentration that it would propagate. I suggest you make a habit of always drilling the end of cracks. This is not just a matter of drilling a hole, though. In the crack on my HRU195 base as reported in the other thread, I found I had to drill one of the end holes half an inch further along than what initially appeared to be the end of the crack. You'll know whether you've found the end after you drill the hole, if you study the perimeter of the hole carefully: there is often a line visible in the cylindrical inside surface of the hole, indicating that the crack continues further. On that base I also had to drill two additional holes along the length of the crack, where cracks had started to radiate in other directions. With all the holes you end up with, you have to examine the edges carefully, and use a small rat-tail file to expand and extend them until the whole perimeter is clear of anything that might turn into a crack.
Now you can see why I put those large angle-iron braces across that crack: I had to ensure that the braces, and their attaching bolts, provided much more rigidity than the base itself did.
Thanks for reporting that crack you found at the rear of your base, where the grass chute runs out, in the same place as the massive one I had. I had no evidence before that mine wasn't an unusual failure mode. As you can see from the way mine had progressed, that crack in your base will destroy the base if you don't do something very effective to prevent it.
