Hi! Did you ever get the diagnosis of a broken valve spring confirmed by the shop? I have a S8 V10 with a cyl 3 misfire and while carbon cleaning noticed that one of the intake valves spins freely by hand. Only difference is that visually it looks like it seals tight on the valve seat but it can be pressed open using a bit of force by hand. Boroscope showed no sign of piston or valve damage. Opened valve cover but wasn’t able to inspect the specific valve components due to the fuel pump assembly exactly like in your case. Engine will be dropped but would be nice to hear how your issue was fixed since I’m having the exact same symptoms. I hope your car got fixed and is running well.
Sorry for not getting back here sooner, life has been rather hectic the last few months. I had it towed to the shop back in February, but he was so back logged that he was unable to get to it until last week. After dropping the engine and borescoping, he found that it’s not actually the valve spring. It appears that the valve seat forced itself into the head, and that’s why the valve was able to spin slightly. Now the head needs to be removed. I plan on heading down there today after work to get an update and see how bad it really is.