A follow up... The level pots were so nasty that no audio would pass except at a few positions, so replaced them and all has been fine for a week of solid 'on' time, no mysterious IOC activation.
Sometimes upon amp power on, one channel IOC light comes on whether there's a signal or not. The signal will distort regardless of level. Swapped inputs and problem stays with same channel. Power cycling the amp several times will clear the problem. The IOC also sometimes kicks in on its own... power cycle will clear it up, usually takes a few cycles. Ideas? Thanks!