Personally I consider it a cosmetic issue unless the barrel becomes truly loose - something I don't actually remember seeing.
The remedy is to remove the rear site completely as it appears to "wedge" the barrel away from the body tube and apply some other type of rear site (i.e. peep, scope, earlier Sheridan open sight.)
I'm assuming you actually mean Sheridan. If you have a Benjamin with that problem then it's quite possible what I'm saying is totally wrong.
In any event, with a Sheridan there's nothing you can do to fix it short of having a pro solder the barrel back to the body tube and in the process ruining the non-replaceable factory finish.