Small oil leak
After setting in the garage for 5 years I recently got my carbs cleaned out and the bike running. During the cleaning procedure she backfired quite a bit. Now she is that she is running I took he for a spin(60 miles). When I got back to the house during my inspection I noticed that one of the Plugs from the top seal of the rear cylinder(right side) had popped out. I pushed it back in and cleaned up any oil and there are no more issues yet. Does anyone have any idea what may have caused this? Could this have been caused by the backfiring? Has anyone else had this issue? Should I be worried? It is the seal just below the heat shield on the rear cylinder on the right side.
Thanks for any help