If the restart does not fix it, you may need a new box. It sounds like the 2.0 downmix of the AC-3 sound pids for this channel is not programmed right; either that or the box is bad. You could post this in the AVS reception thread for your city and see if others are experiencing this. If others post the same issue with DTV boxes, that points to a bad downmix programming error.
Everything else tends to lead toward the problem not being anywhere else but the box itself or the downmix; it is very difficult NOT to get L if you get R, because they are normally part of a single AES stream whenever not part of the AC-3 (where they are again part of a single stream) so it is hard to lose one channel without losing the other, and you have verified that it is not the analog outputs themselves that are not working (they are). One significant point is inside the DVR where the AC-3 is converted to analog; either the channel is lost there due to bad downmix programming, which implies DTV needs to correct their programming error, or a faulty pick-off, which implies the need for a swap.
I guess it could be a problem at the source, but if so one would think that direct reception or other vendors would also see this problem. The fact that old recordings are OK indicate that something changed somewhere, and the most likely spot is not the station's PSIP but how DTV is interpreting that, unless others are not having the same problem over analog outs.
Edited by TomCat, 23 January 2013 - 01:34 PM.