I bought new end caps from Parts4 Engines. I asked Didier in Le Marin to clean the stack and replace the end caps. On re assembly we found the stack diameter of the new end caps was too small. So we had to put the old ones back. Parts 4 engines said they only stock that size.
There was no separate tube. Just the end cap and a push fit inner part.
Any more info on this would be useful.
Ocean Hobo SN96