From another thread I contributed to:
OK, here's the info on when the 722.6 was introduced:
*from 03/95 in the C140 with engine M120 (S600 Coupe)
*from 09/95 in the W/V 140 with engines M119 and M120 (S500 and S600 sedans, long and short wheelbase)
*from 09/95 in the R129 with engines M119 and M120 (SL500 and SL600)
*from 01/96 in the W210 with engine M119 (E420)
*from 08/96 for all MB passenger cars with 4,5, or 6 cylinder engines.