I finally found a replacement for the Stream 2 toilet seat – it’s the Duravit Starck 3 toilet seat. You can find it on Duravit’s website here, and in case it moves the product code is #0006389. It even turned out cheaper than a replacement Bauhaus Stream 2 seat. Even better!
You will also need to buy two M6 6×80 bolts (I used roofing bolts, which worked fine):
These are the same thread as the screws which secure the Stream 2 cover, but will allow you to bolt the Duravit seat in place using the existing fixings.
To unscrew the fixings from above, use a spanner to unscrew them anti-clockwise. The bolts are quite long, and have a rectangular washer on the other end which keeps the bolt in place. They look like this, but the bolts are longer:
If you have trouble unscrewing them (if the bolt is just turning but it’s not getting any looser), try a bit of WD40 and then pull the washer on top up while you’re unscrewing, which will make the nut bite into the washer underneath, and stop the nut rotating.
Once you’ve got 1.5 – 2cm’s gap, you can wiggle the bolt around until the washer goes nearly vertical, and then the whole thing will slide out.
Now, to fit the Duravit toilet seat, follow their instructions but use your new bolts and the old rectangular washer and matching nut. This is what the finished product looks like: