Dang, Bill I should have written it down but I'm going to guess around 8K but it could have been 10K because I was putting on a new rear tire when mine mysteriously died. Pinwall supplied the replacement which is still working (so far).
I thought it was odd that putting a new tire on would make the left cylinder go dead but I think failure is a random crap-shoot. I followed a similar diagnostic procedure and the new (salvaged) CDI was the cure. I was also careful to match the CDI numbers since there are two non-interchangable models: 790 or 865.
My private theory is that the CDI is too close to the left coil and stray voltage kills it. Eventually I'll move mine under the seat (like it is on Bonnies which have few, if any, CDI failures) if and when I can find a cheap salvage harness to butcher .
