Thanks for the post. I certainly agree with you about the innards. That has been my experience with three now. One was quite expected because the outside looked terrible as well. If one is not a do-it-yourselfer, it would be worth taking most any acquired Parker to a knowledgeable double gun smith for that once a century cleaning. Toothpicks are the tool of choice for screw slots and patience helps. It took a hundred years to get to the state the slot is in so it need not be cleaned out in ten seconds. I used a lot of toothpicks on the rib to barrel join and started losing the required patience. I found that snapping a cedar shim lengthwise gave me a very thin, almost knife-like, edge with a thick "handle". That was able to be worked along the rib in long strokes and took out the crud faster than how I had been progressing.
It does take a bit of nervous puckering to get over the idea of taking the gun apart but once you do it, then you do want the unseen guts to be clean as well. Proper tools and lots of questions asked here will get first timers through it.
Cheers,
Jack
The snapped cedar shim tool