Maturin had a note about a c5 with 19 but I haven't been able to see if anyone actually did one. G5 to 18 is obviously a no brainer.http://www.enfieldmotorcycles.com/forum/index.php/topic,10425.0.html
I think a 19 tooth would be a step too far. I'm still uncertain about the 18 tooth on my G5.
What the heck does the oil seal do at the end of the crankshaft? It's inside the crankcase where there's lots of oil and nowhere for the oil to go if it did get past that seal, right? I must be missing something. Great video, btw!