Two to four cups is about as much as we can handle in an hour or less, the amount of time one likes to keep brewed coffee hanging around. Even with keeping in a glass lined "air" hot/cold thingy, brewed coffee starts to break down after about 30 minutes or so, at least this is what one has read.
Am not sure about repairing the C50, but will shoot an email later. As stated in the proper thread at the time, because of the brewing method design, keeping the inside of the lower pot "burnt coffee" free takes a good scrubbing every now and then, and even so there is a layer of "brown" that no amount of rubbing will shift. Suppose one could really go to town, but that might remove the inner coating (or what is left anyway), of the pot as well.
Depending upon price for repair, am thinking it might be best to start with a new or nearly new pot, one that does not have a layer of residue built up that is.
Thanks for the offer again, and will be in touch.
L.