I did this repair pre-emptively yesterday on my 2001 3.0i with 196k miles. Had no problems before or after, and things were in good shape when I found them. Some details:
I used a hammer and block of wood to undo the ring holding the cover on, rather than getting a special tool. Marked with a sharpie beforehand, so when reinstalling, I made it exactly the same. Only needed about 15 degrees of rotation before I could spin it off by hand.
Something I did not find clear in the instructions ... when removing the main assembly, I disconnected the two clip-retained sub-assemblies, leaving them in the tank. I initially had tried to remove it all, and don't know how that would have worked. I basically tried to do as little as possible, especially since this was a pre-emptive repair. Reminded of the saying,
"If it ain't broke, fix it until it is." 
I left that valve, and the seal that AndrewWynn tuned up with Teflon tape alone. BTW, my interpretation of the Teflon debate is that Teflon will not be a problem in gasoline, but many Teflon tapes are not actually made of Teflon, so there's a chance of a problem = not worth it for something that may not even be needed.
My o-ring was in fine shape, but I replaced. Details on sizing:
BMW seems to say this is a 22x2 (ID x thickness) o-ring.
Mine measured as 23x2, probably stretched a little in all those years.
I tried using a couple of o-rings from a Viton kit I recently bought at Hazard Fraught:
20.22 x 3.53 was way too big to fit.
18.72 x 2.62 fit OK, but was maybe stretching the o-ring a little too much, so ...
The head gasket kit I bought a couple of years ago included two
21x2.5 o-rings for the VANOS solenoids. I ended up leaving the solenoids in place (since they seemed welded in place and would not be too difficult to access if they ever did leak), but saved the o-rings. Using one of those seemed like a perfect fit. 0.5mm thicker than the original made it tighter, but not difficult to install. Happy with that solution.
I read the full discussion on using the zip tie, concluded it was worth doing, and did it in less time than it took to type this sentence. In case anyone needs this number, the
thickness of the zip tie I used was 9/64" and it was a pretty perfect fit. Installation was easy and I still don't fully know what the assembly looks like. Just fed the zip tie in the gap and it routed around easily so I could finish the installation. And unlike the Teflon tape repair, I don't think there is any chance the zip tie would cause a problem.
Overall, things seemed really well built throughout. Plastic did not seem brittle, things came apart and went together pretty easily. I was having no problems at 196k miles and 19 years, so hopefully most people never have a problem with this pump.