Rebuilding dash gauges

[Pat Leask <pleask@shaw.ca>]

The winter is for working on our cars.. right ? Well, one thing leads to
another and I've pulled out my SMITHS gauges. I have taken that lock ring
off and it would appear that there is a huge "O" ring that fits inside the
front locking ring (Holds the glass in) but has crumbled to dust.
 
Am I right ? If so, where do I get such a thing for the smaller and larger
gauges ?  Any options ?
 
Thanks, Pat