What's wrong with the existing rules?
A full MASC 'Mech battalion activates the system to try and get a tactical advantage and 1 Mech just freezes (on average).
It's not nearly as bad as, say, HVACs, but it's still an equipment that seems much more appropriate in a Solaris arena than on a battlefield with regiments of 'Mechs, where a minimum ~3% "self-kill" failure rate per activation is not exactly trivial. Of course, on Solaris you have TSM...
More importantly, the MASC failure system just isn't... fun. RACs can be interesting to manage since you manage the jam chance with your rate of fire, and the jams are a temporary and fixable issue. Things like the RISC hyper laser get a pass since it doesn't pretend to be a mature, viable system. MASC failures though, I can confidently say those have never added to the game's enjoyment when I've played, on
either end.
As for house rules, when playing online MM has that unofficial "Kinder MASC" or something which I use. Basically makes the avoid failure countdown start at 0+, failure-free on the first activation. Kind of makes MASC a sensible Mech-scale WEP (War Emergency Power) or an afterburner, a nice boost but not something you want to have active all the time. With that rule, the more conservative players can get good use out of the system, and the daring players can still push their 'Mechs to the limits with all the risks that entail. Overall it feels more like you're managing a system and if your Mech goes kaput it feels more like it's your fault that you pushed the 'Mech too far and less like you're playing Russian Roulette by activating MASC with your war machines.