If you are wishing to go inside the amp or if installing a used one is your plan, then the easiest way to do it is to remove the electronics from the aluminum shell and leave it in place. Substitute the guts if thats the plan.
Personally the unit is such a POS, that I would suggest a new one as the price keeps coming down (MB list is 260 currently for 023 545 21 32) and the number is changed again. I believe the newer units are doing a better job.
Bosch Master, ASE Master, L1
33 years MB technician