D315 opinions and help

Hello all,

Those of you that have read my past posts know of my BE 15-B with a D315 and the constant popping sound coming from the exhaust and the pony in need of a complete overhaul.
I finally got around to getting the pony and the cylinder headed lifted off last night. I have to say I am very confused. I have worked on engines my whole life so not a newby by any stretch.
I was expecting to see a burnt valve or some other blatant evidence of what was happening but no such luck. With the popping sound coming from the exhaust, it also emits a moderate amount of fuel slobber out of the 3rd cylinder exhaust. All of the pistons look great, cylinder walls also. It has no blow by, no water in the oil. The valves look great as well as far as I can see. It may still be a bad seat on the exhaust valve, I don't know. The old engine sat for probably 15 or 20 years and was locked up when I purchased the rig.
Any opinions at all of what it might be?

One fellow here had a D2 that was popping and just the other day, he corrected the injection timing (lifter height) and apparently that stopped the popping. Fuel slobber might indicate a weak injector on #3 so that might need attention