Your best bet (which isn't what you wanna hear) is to remove the gearbox fix the damage with NEW parts and re-fit.
Granted it might take a bit longer but you'll know it's running right, you or your gearbox man might find other issues that need fixing and fitting another 2nd gearbox might be pointless as it could blow within 10 mins of fitting it.
Do it right, fix it, put up with the van for a few weeks and know that your gearbox has been repaired correctly, rather than sticking in an "unknown" gearbox.