I don't remember an o-ring. Did you buy a genuine BMW tank ? If not, try and get a refund. Apart from that fitting, there is a magnet on the underside of the float and this can misalign with the sensor to show it's empty when it's not (after refilling)

 

thanks for swift reply champion, ideally a BMW part is warranted but very expensive but I purchased a tank from europarts at a competitive price with extra discount--never had any problems before with items purchased,but knowing my luck I`ve picked up a dud.

 

I bought an expansion tank from Euro Car Parts, it was a Hella one. Exactly the same problem as you're having right now (looks like a leak from level sensor but isn't), turned out the expansion tank was bad, so I got one from BMW and there were no more problems.

 

and I thought that was only me. getting the duff new stuff !!

 

When i , i think it about stg£70 on Amazon but i got the genuine article for about eur?110.

I bought 3rd party products on the "assumption" that BMW are ripoff merchants. I actually bought a new battery from BMW last year. It was only about 20% more expensive than a never heard of brand one from my local motor factors.

So it seems to me that BMW parts are around 20% more expensive but it's worth it to get it right first time, and for the part to last and perform as expected.

It's on labour that they clobber you if you get them do something.

 

some things are cheaper from main dealer others if you get oem from euro car parts or gsf work out cheaper