I've ALWAYS seen 2.2 & 2.0 qts referenced for a refill. The larger #'s are for a dry fill. The real problem here is ppl consistently fill the trans fluid wrong, document their incorrect method, then other ppl follow it without ever checking the correct way for themselves. FWIW using the correct method to fill removes any question of amount. The amounts quoted are useful only for considering how many quarts of fluid to buy before starting...they have nothing to do with filling. If you're significantly off from the quoted 2.2/2 qts its also an easy way to identify a larger problem.I've got the same question as cyclehead as no one ever really posts fluid amounts of a c60 w/LSD as 2.0qts and 2.2 open diff. All numbers I see are "2.4 and a bit less for LSD cars" so I've put in 2.4 in my LSD c60 for racing and she's felt fine.
You fill using the fill plug, until it drips out of that plug...with the car flat & level. Put a little vinyl tubing on a funnel, the trans fluid goes down slow due to viscosity/tube size but it really isn't any more work once you're accessing the drain plug from below anyway IME...you should loosen the fill plug first regardless, then just stick the tube in there at the same time. 1 extra time sliding under the car to tighten the fill plug & you're done.