Until it's sorted out, everyone is "winging it", but you're suggesting a top to bottom rebuilt for what can be "one bad receiver".
The no packets problem I think is due to the router and ip addresses. There is an error code that pops up on the dvr but if it's intermittent they may not be using the dvr when that happens.
Again it's not as likely but given all of the smaller items getting everything to spec would remove possibilities that could exist.
I don't disagree with your line of thought on the whole issue but I also don't want to ignore other possibilities that are easily, and should have, been resolved by now.
I hate "shotgunning" to try to fix things, but sometimes that's all you've got left.
Since the DVR has recordings that don't want to be lost, setting it aside, installed another DVR and testing it in service to see if everything is fine or not, might be another option.
If there still are problems, then it wasn't the DVR. If they've gone, well it more than likely was.
If a DVR is not recording the right channel, then it has nothing to do with the router.
If it's not having recording problems, but playback issues, but only with the CCK connected, well it's the router.
Following a logical troubleshooting path to isolate the cause(s) should be followed "IMO" before you rip out the whole system, because one tuner isn't active and the customer doesn't care.
"But hey" that's me.