I'll do the soapy water test. I have read that the staining around the plug could be "soot" from the combustion chamber - more likely than the impossible "oil" I've been imagining. Member Prue 1 brought up the topic in 2014. Fred and RG gave some opinions on its source.
The response here has been, as usual, excellent thank you gentlemen. As I indicated in post #29, the starter has become my primary concern and, as the plug issue requires the use of untried and possibly inadequate skills, I will hold off that project for the moment until I've checked all alternatives.
Time to remove the starter eh? You know, I looked at the bloody thing a half-dozen times when I had the motor out and considered stripping it down - would have been a damn site easier. Obviously, lack of confidence and impatience don't motivate common sense.
Some research, purchase of seals and maybe 4th gear assembly and take it off. I know INXS posted some good info on the starter system back in 2010. Do I detect a note of sarcasm in your responses, Gary and Griz??