Ignition Check Irregularity

No, Roger, this problem is recent and unrelated AFAIK to the plug and cap replacement.  I will fly this morning and try and jot down more specifics.  I appreciate your thought that it might be one plug, but the on/off nature of its occurrence--particularly post-flight--runs contrary to my experience.  My airport is uncontrolled, and taxi time is pilot optional.  Has anyone ever had a similar problem that traced to those intricate little plastic thingamabob cubes that connect to the modules? 

When my first module died, it just went dead.  Period.  Died in its sleep.  A Rotax technician told me sometimes the modules fail progressively.  Does anyone think this rolling RPM drop is indicative of a dying module?  I don't mind throwin' $3 sparkplugs at a problem but a failing module after less than 200 hours...  Well, Austria is a long walk from Texas to give them a piece of my mind.    Again, thanks to all for your suggestions.   Jim

I am having difficulty with this RotaxOwner site's response mechanism, so if I am redundant here please forgive me.

Addressing your thoughtful responses: A solid "no" all of Mr. Griffin's inquiries regarding modifications to the plane.  The answer to Roger's questions: No, this problem came up nearly 100 hours after plug and cap replacement.  It is a recent phenomenon.

I flew the plane today--ambient about 50F--and noted the +-300RPM miss on Module B--before and after flight.  Minimal drop on A.  B is the new module.  This is the same, maybe slightly worse roughness I experienced before installation of the new module.

Before I start checking the plugs, I would like to explore any other possibilities y'all might have come across.  A Rotax technician once told me the failure characteristics of modules vary from gradual to complete no-go.  Does this comport with your experience?  My "A" module just plain died a couple years ago. Nothing...apparently died in its sleep.  I replaced "B" recently because it had over 1000 hours, but the roughness continues.

I'll pull the cowl and run it on the bad module and see if one jug is lukewarm.  Then check the plug and cap.  Beyond that medieval trouble-shooting, I'm out of ideas.  I don't think this is fuel and it's definitely only on the one module, which is a new one.  Maybe the wiring in those fussy little plastic cubes?   Thanks in advance for your thoughts.   Jim