How did ypou go with the O ring? Are you referring to part 11 of the attached picture? If so there are two different o rings for Cougar. 1 for 1/6/1999 to 31/07/1999 Part number XS8Z 9276 AB. 2 from 1/8/1999 on part number XS2Z 9276 AA. If you let me know exactly which one you need, I can do a bit of a search to see if anybody has any..
Cougar Fuel.pdf
Cheers.
PS sorry for the late post and hope you have fixed your issue, just saw it and willing to help if required.