Right Mag Only Rough Running

I know there a lot of topics on rough running engines but I did not find one that mirrored my situation.  So if you'll please be patient with me.  (first time Posting here)

I have a 912 ULS manufactured in 2010.  It has roughly 585 hours on it and a little less than 40 hours since January.  It is installed in a Piper sport Cruiser.  The engine has been running fine with no major operation problems until just recently.  While completing the Mag checks prior to flight the engine ran rough during the right MAG check (ENG RPM 4000) .  The drop was normal, about 110 RPM.  The same drop as the left MAG but the left MAG ran smooth and the engine runs smooth in both.  Eng starts fine.

Troubleshooting so far: 

1.  Visual inspection of the plugs and leads.  All plugs are tan in color and dry.  Inspect good.  The wires and leads look fine no obvious corrosion or damage.  Reinstalled plugs swapping top to bottom.  Initially on first start the engine ran fine and the MAG checks on both were good.  The engine ran smooth.  So we shut it down and let it sit a few minutes and started it again but this time the RT MAG again ran rough. Left and Both were smooth.

2 Disconnected connectors and swapped the Electronic Modules.  The connectors are clean and no damage as well as the modules.  These are the newer style modules with the 6 pin connectors.  Started the engine and completed a Mag check with the same results.  The fault did not follow and the engine ran rough during the RT MAG check.

So I am now trying to decipher the MM and calling upon you all if you have any experience with a single mag issue.  I am leaning towards a plug lead or one of the Dual Ignition Coils.

Your input is appreciated.

Mark Keiper  mdkeiper@gmail.com