Gerald,

They are a regular o-ring.  They get flattened by time and age.

Hope this helps,
Ken Wilford
John 3:16
www.vanagain.com

Gerald Masar wrote:

>In an '88 Westy AT, is the seal for the coolant level sensor in the expansion tank a
>special o-ring, or just an ordinary o-ring that has taken on a flattened look because
>of where is fits?
>Thanks,
>Jerry
>
>
>