I would make sure that there was no movement in the high shear rivets that attach the bearing block mount lugs to the stringers. Other than that, as they say, nothing to see here....all of the other mechanicals for the tail need to be accessed by removing the tailcone fairings.
Thanks for the information. If I peruse this plane or end up buying it we would replace all the hardware with new and make sure there isn't any corrosion. It Is hard to see in the picture but on the right side of picture there is a small spot that may be light corrosion on side of fuselage.
Very recently during the annual inspection I cleaned out all the open compartments with Stoddard Solvent (aka Mineral Spirits). it's a wonderful engine cleaner and works very well in sections like the tail you show in your pic. My tail cone section looked much the same. I was able to carefully climb in there (with a tail stand in place mind you) and spreading my weight across the stringers I spent a good bit of 2 days cleaning out the tail cone with Stoddard Solvent rags and a vacuum. Mine looked very much like the pics you show but once cleaned out it looks like the factory zinc chromate is in tact and it just came out of the factory (almost). Here are a few after pics. With similar effort I imagine you will find this 400 also comes quite clean. Incidentally I was shocked how many old screws, washers, spiral drill shavings and rivet heads I found rattling around in there. Like you I had a touch of light surface corrosion on the lower part of the stabilator tube. Some scotch brite and zinc chromate took care of mine.