Chuck McCabe, I just finished fixing one from a buddy's shop. Same issue, no matter what it would only brew 4 oz at a time and took forever to do so. I did a few things. First I removed the plastic holder that holds the K-cups.
This one is simply pulled straight up, but had a bit of resistance from some spring clips.
On the bottom of that is a tapered needle that pokes the hole into the bottom of the K-cup. On the side of it is actualyl a small hole. Use a paper clip (or in my case I used a needle) and stick it in there to remove any scale, coffee grounds etc. As you can see from the first pictures, there will be a lot of coffee in and around it.
Next you need to clean the top needle. It's a bit trickier since it is somewhat hard to reach around the sides. So open the Keurig all the way, and again use a needle or paper clip. There will be three holes around the needle.
At this point I tried to see if it would finally brew a 12oz. coffee which it did not. Next I concentrate on the water intake. Remove the tank by simply pulling up on it
On the bottom of the tank is a filter and a check valve. I removed the three Phillips screws from the filter and removed that from the tank. I cleaned it with some running water and an old toothbrush. It's a bit tricky to remove since you will need a long Philips screw driver. As a finally step I wanted to check the water supply to the needle for the top of the K-cup. If you take a look at the part where the top needle is mounted, you will see two Phillips screws that hold the top cover on. Remove those.
Slightly lift and pull the top cover out.
with the cover removed you can see where the water comes from the boiler through a check valve and then to the K-cup Needle.
If that check valve has scale, sediments or other contaminants in it, it will not let the water get through properly. Unhook the check valve from the connector above the K-cup needle and remove the tie straps. Now you can remove the check valve. Try to blow in it from the boiler side and it should open. Do that a couple of times to loosen any sediments etc. I also run some hot water from the K-cup side into the check valve and shook it up. I did get quite a bit of debris out of that. Once I had it cleaned, I reassembled the valve, hoses and cover. I did replace the tie straps as well. Once fully reassembled, I did get the Keurig to brew 12oz 25 times in a row:-). Guess I fixed it. Biggest issue with this repair are the need for a long Phillips #2 to remove the screen from the tank, and to reassemble the two screws for the top cover. I did turn the Keurig upside down to get gravity to help me reinsert the screws. Hope this will work for you as well as it did for me.