I have a '79 300SD and am having trouble getting the old seal out as well. For my engine the MB manual says to use a screwdriver to get the old one out and the special puller to get the spacer out. I'm not sure if yours is the same.
I've used a screwdriver, needle nose pliers and various picks; sprayed things down with carb cleaner and PB Blaster but I haven't been to get the old seal out.
Still working on it.