@roymil: I've owned the Coupe since Apr '92, and have never changed the diaphragm. On top of that, the car sat "stored"(poorly) for 10yrs from 2009 until Jan. '19. So along with rebuilding the fuel pump in Jan. '19, this was on the laundry list. But to answer the other part of your question, no, there were no running issues. Surprisingly, the old diaphragm was still quite nice. It was a little stiffer than the new one, but still pretty good. My hunch is that it was replaced at some point in '90-'92 prior to my purchase, because the car had become undriveable. It would run for about 30min, shut down, and could not be restarted for hours, or until the next day. It had been to umpteen shops in the SF Bay Area, and no one could figure out what was wrong with it. So the owner sold it.
@wwheeler: I don't want to post my Coupe shenanigan's to the W113 area. It's nice enough that they even allow a Coupe owner here. Cool idea to do that long bolt trick. Was that something shown in the big blue book? I installed the cover by slowly finger tightening the bolts in a rotating X pattern, hoping to achieve the same thing, and letting that inner metal hub settle down over the fitting inside. Now you have me wondering if my method was wrong and I wound up clamping down the diaphragm all wavy/wrinkled. Shoot, I better pop it off and redo it. Hope I haven't ruined it.
Now if I could just get the radiator back!!! I'm really looking forward to driving the car, especially with the FI linkage dialed in. The seatbelts arrived today and the sill mats arrived yesterday, so at least I have a couple fun jobs ahead.
