I'd put it in a bench vise with a piece of wood (soft pine/etc) on both sides to try to correct it.
I don't have any problem with my black or yellow silicone washers sealing. If anything it's the rubber ones that seem to harden more as they age whether in a hose or still unused in the locker I keep such things in.
On a related note it might not be that the end is oval now that makes it leak, but rather that the very end is not flat. To some extent you can correct that with a file, finishing up with a piece of sandpaper on a very flat surface, then I would use a piece of steel wool to debur it but the sandpaper could be used for that too.