I am trying to rebuild the clutch slave cylinder for a a7245. The search for the O-ring has been interesting. I am down to the large one on the end of the piston. I have given up finding one shaped like the original and now would settle for a regular shaped o-ring that would fill the gap on the piston, inside diameter fit the piston and outside seal against the cylinder wall. I know this is not ideal but the idea is to have a backup that will work while a new cylinder or rebuild kit is ordered. These seem to fail with some regularity in cold weather. Any suggestions or thoughts would be welcome.