keep in mind that it will all vary depending on what class you are using when testing - Rogues and Warriors will not have any spell crit to speak of - compared to Paladins
ie: https://rogerkarlsson.com/static/blogs/wow/lifestealing/lifestealing-rogue.gif
from the first link https://rogerkarlsson.com/blogs/wow/lifestealing/
unfortunately, this Paladin doesn’t say whether he got crits or not from his Lifestealing procs from the blog comment post:
Noen writes
9 thumbs
Sorry for a slightly misspelling in last comment, I ofcourse mean attackspeed, not attackpower.
However, I got myself lifestealing on my Hand of edward the odd, and started beating up people in stockades.
Here is the result after 5 minute combat with seal of crusader:
235 hits
34 lifesteal procs
9 heroism card heals
8 maelstrom lightnings
And without the seal of crusader:
181 hits
26 lifesteal procs
9 heroism
3 lightning strikes
Using the Chance to hit(%) formula, I expected:
22,625 lifesteal procs without seal of crusader. (1.60 attackspeed)
20,915 lifesteal procs with seal of crusader. (1.14 attackspeed)
So it seems like seal of crusader boosts the proc rate 
# 4 Sep 2006, 14:56