Hopefully this will offer someone in a similar predicament some encouragement. We dug up the soil pipe between the septic tank & dry well yesterday. I am relieved to say that the problem appears to be a failed soil pipe just before the dry well. About a foot from the dry well, the pipe had failed and there were some large chunks missing. The pipe was almost completely clogged with debris, roots and so on. We discovered that the dry well had a cover, and the level wasn't full enough to cause the lack of flow from the septic tank. We did replace the failed soil pipe and I have added a baffle into the septic along with a clean out.