Neumann, I'm sorry, but I checked my file of receipts and can't find it, but I did make a notation in my maintenance log that the part actually cost me $32, and it came from the dealer.
It's right behind the brake master cylinder on the firewall, and it has a black line (electrical) and a green line (vacuum) going to it.
Having said that, the same code eventually came up again on my car (#26), and my mechanic, Enrique at Mr. MB Motors, ended up replacing another part with the same name (upshift delay valve) and also replaced the bowden cable (transmission cable). These are located on the transmission. His comment was a code #26 is usually caused by a faulty upshift delay valve, and it is the part that is located on the transmission, not the part that is on the firewall, and it cost about $250.00
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".