Oh well...if it happens again I'll get in touch with Sound Devices. I have to send it in to get the rechargeable battery mod anyway...
have you tried using rechargeable AA nimh batteries on the fp24....i believe these stock units already have this mod built in.
i believe it was the older mp-2 units that needed the mod, but the mixpre's should be ok.
if not its only $35 to get it done, and they will recalibrate it and check the pots for free (if you ask). sound devices has very good service and turnaround time. make sure you call sd in advance and get a work order # prior to sending it in.
i have never had a problem as you discussed although it seems my channel #1 (left) always seems a little lower than the channel 2 (right). i noted this to sd when i sent my unit in for the nimh mod, and they checked it out and said it was ok. maybe it was a matter of where i was set up in the hall??