Sad news indeed. I probably wouldn't have heard of it until years after if you hadn't posted about it. Now I *really* need to find part three somewhere. It's weird, but it's the only part no bookstores stock. And when I order things, I tend to never find time to get them.
His books were among those I taught myself (proper) English with. Someone had lent me a big book with the first four parts in it. I read it during a holiday in Bavaria and it's one of the things that made that holiday two of the most important weeks of my life.