foookin heck found a huge crack

There was one other similar TLS case I saw pics of once long ago, on tlplanet and probably still migrated to here...

What do you mean by "not even thru the weld" it sure looks like it's all exactly thru the weld. What does the other side look like? That's an unbraced (not TLR) TLS swingarm right-side up, with the rubber chain snubber removed? So that's the chain side that broke? I'd speculate that it's suspension issues, differences between the springing and damping or simply maintaining wheel alignment rather than chain tension vs. braking force. I'd speculate this results from hitting a pothole, or jumping the railroad track crossing, something like that. Otherwise N2wheelies high compression drag bike with the slightly extended swingarm would have been at risk.

I just exended my TLS swingarm, adjustable from about stock to about +5 ???? and was debating whether to swap in a TLR swingarm. So these pics have got me a bit alarmed. But...I suspect when you bottom out the rear suspension hard the SOAS linkage stops before the connecting rod to the rotary damper crank, so that could be where it would break first. IMHO the stock rear spring is too soft for one rider, much less two. Did you ever hit a pothole hard enough to bottom the suspension with a passenger? Ever bit anything hard enough to bend up a rear rim?

I guess I'm not too surprised you didn't feel it since it didn't break off yet. My rotary damper was pretty damn loose and I never noticed that either.

So what are you going to do?