Damn Richie, for that kind of time and money you could almost have a major tune done! When mine was idling a little rough, my tech carged me for a spark plug wire connector and 1 hour diagnosis - problem fixed. I'd take it to a good independent first.
Before I gave the dealer that kind of $$$ I would check the search button on rough idle and see what others found. I would be inclined to check plugs, cap and rotor, plug wires and connectors, fuel filter, and O2 sensor, and fuel pump if all else failed.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E