This may be related or not.  I reported arcing rectifiers on my tori long ago using the stock ruby's that came with it (1.5 years ago?).  I was comparing left and right channels by turning the power off and on alternately per channel.  I'd notice arcing in the rectifier on power up. I realized this never happened when the amp was cold (off for quite a while).  It only happened when powering on immediately after powering off.  The only differences I can think of between the 'cold' vs 'warm' scenarios are some caps still have a charge in them, and all the cathodes are still warm too.  My solution was: don't power cycle the tori in short durations like this.  No arching with normal use.  No dead rectifiers yet.

My se84ckc has the 274B in it.  never see it arc.  But guess what, I just tried it. I just turned it off for 1 second (it's still playing music actually).  turned power back on, and there's a tiny amount of arcing.  

for me, any of these rectifiers arc when powered up shortly after powering off (ie: when you're looking for an arc).

Anyway, I just don't do this anymore.