[Jamie '92 968]

I plan to keep accumulating data on when it happens and when not to try to establish a pattern. Last night and today there was no sign of the dreaded "shudder".
My best guess at a pattern is that it may be more common when the weather is wet, or was wet the day before. I'll need more data to establish a pattern for sure.
I may also try to chart it by astrological sign. I believe my car was originally delivered in February, so is may be an Aquarius, or possibly Pisces.

I'm also going to replace the plugs, since it's been about 42K miles and 4 1/2 years, and they are cheap.

Flash, I guess the oil on the clutch theory is a possibility. Any suggestions for a conclusive diagnosis or remedy short of replacing the rear main seal (I was hoping to wait and do it with the clutch someday)?

Also, I thought the min octane was 93, which has been hard to find lately, and had been feeling uneasy about using 92. I also put a bottle of octane boost into the car when the shudder first appeared as a test, but to no effect.

Someday I'll again be able to aggressively hit the accelerator with a sense of excitement rather than dread...