In the current BattleTech Total Warfare ruleset, MASC still has a chance to do that, but it's not fixed like it used to be years ago. Instead, a critical hit is rolled on each leg, making it possible that something else besides a leg actuator will take damage due to the stresses placed on the leg. So anything in the leg can be damaged, like jump jets, or even ammunition.
For the upcoming Shadow Cat and Executioner, we only have to worry about losing leg actuators and jump jets. For any other 'mech that can mount MASC, just be careful where you put that ammunition, or else you may lose your 'mech quite early in-game

...Well, that's if the developers go that route. Currently we don't have any critical hit effects from damaged leg actuators, and we're waiting to see how they're going to implement MASC, which Russ said we'd find out this month.