Well, corrosion is of a problem in any calculator with NiCd cells. But you're right, for some reason these 30-series machines seem to be more prone to it than others. I once received a 33E that was stored in its case for years with a set of partially dead batteries inside. When I opened it, there was white crystalline stuff (potassium carbonate, probably), tons of it, even on the outside! The flexible cable connecting the battery contacts to the power supply PCB easily rots, too.
The only other machines I've seen that are as prone to corrosion are TI's third generation scientifics, like the TI-55 and the like, with the BP-7 electronic battery packs. In those, battery packs, the circuitry tends to rot away completely.
As for opening a 30-series machine, until today I'd have been one of those suggesting that you really need to pull the case apart with force. (Worked for me so far without breakage.) However, I just read a post here that suggests that it is possible to slide the case apart after all, without applying excessive force. I'll give it a try.
Viktor