So far no one has replied that they have seen an actual doo hickey failure. So is it just mass hysteria?
Bliz, Generation I doohickey failures, even catastrophic ones with massive collateral damage, are not unknown. Thus, I wouldn't categorize doohickey concern, overall, as "mass hysteria," myself.
Since the '08 model year introduced a more robust, redesigned doohickey, I tried to limit the scope of my query to Generation II KLR650's; note emphasized words quoted:
. . . anyone know of a valid report of a catastrophic doohickey-related balancer drive failure on any '08 or later KLR650?
Limited-tension spring reports abound, but--any incidents of late-model doohickey failures grenading any engines?
A slack spring comprises a deficiency, leading in time to excessive vibration, undue wear, and possibly even serious component failure if not corrected (or, as mentioned above, compensated for by manual drive chain tension adjustment on a timely basis).
While a BROKEN spring can wreak havoc with fragments disrupting engine innards, a slack or broken tension spring doesn't pose the imminent hazard of a broken doohickey. Even without a tension spring, some drive chain tension is maintained by a properly-torqued intact doohickey, with hope for a "fail-safe" condition. With a non-functional doohickey, nothing contains balancer drive chain tension, free to vary over the complete adjustment excursion, resulting in the vibration and wear mentioned.
I wondered if the more robust Generation 2 doohickey appeared effective in reducing the catastrophic disasters previously experienced in Doohickey-Land on the Generation II KLR650's.
Now, should YOU upgrade your doohickey and/or spring on YOUR Generation II KLR 650?
As Clint Eastwood once said, as "Dirty Harry," "Do you feel LUCKY, . . . ?"