As I'm sure many of you are aware and most likely long ago complied with, Rotax issued a Service Bulletin (SB-912-043-R2 and (SB-914-029-RB) back in November 2006 which in part called for replacing the radiator cap part no. 822075 (0.9 bar) (13 psi) with a new radiator cap part no. 922070 (1.2 bar) (18 psi).

Perhaps you just wish to replace you cap because its been 10 years and it does have a rubber seal. You can buy one from CPS for $84 or Lockwood for $70. Or much better still for about 1/2 that cost you can buy the same cap online from a BMW motorcycle parts dealer. As you might have seen on the Matronics email list, The single cylinder 4-stroke BMW F-650 liquid cooled engine (1997-2000) was made by Rotax and uses the same 1.2 bar cap.

The BMW part number is 17112345074. I just bought one from Rick Johns of BMW Motorcycle of Escondido, in California.
http://parts.bmwmcescondido.com/p/BMW__/Radiator-cap/42783598/17112...

For less than $40 it's an exact match for 922070 both in appearance and fit.

Blue skies and tailwinds,
Larry
CH601HDS