I hope ishipaco doesn't mind me posting
this PM he sent to me.
Part I sent to him: "I just purchased a used 40e and will be using the seal replacement instruction on our website, but had a question about the membrane. Do you know the dimensions of this membrane? Would this replacement fit?
Thanks again for the great website. The confidence I gained by reading your website is one of the reasons I went with a 40E."
"I'm afraid (1) I've never taken measurements of the membrane element, (2) I don't recall ever seeing either Recovery Engineering or Katadyn publish those dimensions anywhere, (3) since our boat was destroyed last winter, I don't even have a membrane I can measure, and (4) the membrane used by Katadyn, as far as I've been able to determine, is a proprietary part (like the drive belt for our old Autohelm 3000 Autopilot!).
Here's what I can tell you:
1.) Be very careful trying to use third-party membranes. Ones I've seen in the past (e.g., from Village Marine) were a poor fit.
2.) The one I saw at the link you sent looked like it wouldn't work, because it has nipples on both ends. The 40E membrane (which is the same element used in the models 35 and 80E) only has a nipple on one end.
3.) If you are determined to purchase a third-party membrane, I suggest you obtain measurements from the old membrane in the used unit you bought. If that's not possible, you can try to find someone else in the fleet who has a 35, 40E or 80E, and get your measurements that way. Of course, that assumes a friend who is willing to partially disassemble their watermaker in order to help you.
I wish I could tell you more. Sorry. Good luck."