The seat had suffered some cosmetic damage way back in the late 1990’s. Also, the cover had started to crack in a couple places. A new seat from BMW is $376. A custom seat from Corbin or Sargent is even more.
I bought a new cover from Northwest Classics in Canada (via eBay) for about $70 including shipping.
The seat foam is supposedly attached to the original cover so it is recommended to install the new cover over the old one, which is what I did. You can use staples or pop rivets, but I didn’t have a suitable staple gun and I thought the rivets would work better. The plastic seat shell is about .080″ (2 mm) thick so I bought some rivets what would squish down to about .125″ (3mm) in length. They seemed to work well. Drill a .125″ hole through the cover and the shell, insert the rivet and collapse it with the tool.
I taped a metal spacer onto the drill bit and chuck so that only about 1/4″ was exposed. I didn’t want to drill through the old cover, the shell, the seat foam, the old cover again and (game over) the new cover.
The cover had a white chalk line on it where it should align with the edge of the plastic shell. I attached the cover at the front and back and then stretched it side to side and riveted it at the ends of the seams. Then stretched and riveted as needed to get the cover tight against the old one.
I used a heat gun to make stretching easier, but it would have been better to do it in the sun on a hot day, I think. Also, the stretch for the first of the side rivets later became insufficient as I had to gradually stretch it more to get the cover tight. The cover seems to perform just fine, but I can imagine needing some flat washers to prevent critical rivets from tearing out.
After the seat was on, I had to clean and wax the rest of the bike to match the new look.