they are notoriously weak. My diff broke up whilst driving along!! quite unpleasant. Hubby dismantled the GB and and rebuilt it, but it was never quite the same, eventually we bought a crashed car and he used the GB from that, it's fine now.
since then we have broken a couple of multis we have an ebay shop UglyBugBits. No gearboxes at the moment, they get snatched up, but we will get another car soon enough, so it's worth a check.