Most of the old typewriters have heavy cast aluminum shells that are worth taking the time to remove. There are other large pieces of cast on the insides that can be a pain to get to, especially since I only have the patience to get one cleaned down all the way. If the internal pieces are big enough you could take an angle grinder to them and clean them up faster than taking all the screws out. Still, at least get the shell off.

Also on the oldest electric types there is a decent sized motor inside.