I'm replacing the diaphram on my 260e, too. Eventually might have to dig inside the dash and remove it... (ugh)
Anyway, I'm sure Fastlane has the parts (and they're great to work with) but there's another website that sells the rubber diaphrams for $5/each.
You might check them out. Very nice (as is Fastlane) and very prompt. Mine should arrive tomorrow. I'm fixing the defrost flaps first... then if things aren't cool enough to fight these Central Florida summers, I'll dive into the dash and replace the one for the "fresh air flap."
Please keep me posted on your progress. Maybe we can help each other out through email. Do you have the repair cd?