The shock is, for all intents and purposes, vertical, relative to the body when at ride height. The bending moment on the nuts is not significantly different to the stock mount. I'll repeat: shock/abuse loads (pot holes) will cause crack initiation here. Without a sacrificial failure point, this can happen with said loading. Accept it and install the part or move on and keep the less-than-excellent ride & performance of the stock mount.
I disagree, there is a difference, and it's significant. I'm not going to bust out my statics texbook and start drawing FBDs here, but there is an obvious difference in where the force is acting on the mount relative to the OE design which is pretty much right between the mounting bolts, just a little bit above CL. If the system was actually vertical, perfectly rigid, and the bolts acted in pure shear it wouldn't much of an issue, but the mounting face is at a slight angle, maybe 10 degrees off vertical, and there's probably a lot more movement even in stock form than we realize - it's just sheet metal after all. The BMR design moves the force acting on the mount upward close to 3" and slightly further outboard, taking what is probably a 1/2" lever arm from the OE mount and changing that to a roughly 3 1/2" lever arm. That could easily increase the reactions at the mounting bolts, and under the right conditions cause a failure.
I'd encourage you to take the measurements and do the FBD. Go to the next step and factor in contact area for the load to be distributed to assess stress. No, they're not in pure shear but also not nearly the bending load you're thinking. Installed like that (as at least one of the two failure cases was, sans bumpstops), it's a recipe for failure for a street driven car. I have 10k street miles, over 10 autocross events and a handful of track events with them and there are no issues. Maybe it's the higher rate rear springs, and/or the combination of FP track shock damping rates and trimmed stops, but I cannot say I've been too kind and they've seen plenty a rough road and bumps.I disagree, there is a difference, and it's significant. I'm not going to bust out my statics texbook and start drawing FBDs here, but there is an obvious difference in where the force is acting on the mount relative to the OE design which is pretty much right between the mounting bolts, just a little bit above CL. If the system was actually vertical, perfectly rigid, and the bolts acted in pure shear it wouldn't much of an issue, but the mounting face is at a slight angle, maybe 10 degrees off vertical, and there's probably a lot more movement even in stock form than we realize - it's just sheet metal after all. The BMR design moves the force acting on the mount upward close to 3" and slightly further outboard, taking what is probably a 1/2" lever arm from the OE mount and changing that to a roughly 3 1/2" lever arm. That could easily increase the reactions at the mounting bolts, and under the right conditions cause a failure.
I think it's disingenuous to simply say "accept it and move on" or disregard this failure as a pure fluke when it may preventable. What I'm seeing in those pictures is fatigue cracking, and that begs further investigation. I'm not bashing BMR here, I like and use their products and I'm using these mounts, but I'm interested in figuring out a way to mitigate the risks.
Very glad to hear you haven't had an issue, I'm only on the FRPP track shocks which shouldn't be as aggressive as the Vikings, and I doubt I'll go to anything more aggressive in the future. I'm on Steeda adjustable rear springs, they're a pretty high springrate and set fairly low, so I'm thinking about taking the boot off the shock and running just the bump stop and mounting a GoPro somehow to see if that shows anything, excessive bump or anything flexing.
Most certainly not. A riv-nut there would probably add some robustness for sure.