Well, finally got time to take it to the mechanic. The rings are the culprit. I asked them to do a leak down test. Before that they decided to stick a borescope in the cylinders. They saw signs of ring wash. Combine that with the fact that it is hard to start when its warm and the shop was 99% certain. Didn't even bother doing the leak down test.
So, looks like I have a decision to make. Rebuild the 340, or build up a 440.
