Spark Plug Tubes o-ring replacments availabe?

[Johnny_5]

Since I have the valve covers removed I figured I try to change out as much as gaskets, O-rings, seals, etc as I can. My tubes appear to be fine and would like to replace the O-rings on them but I don't see BMW having this option available. Does anyone know the sizes or have changed the rings or do they just purchase replacement tubes? I don't have any oil in the spark plug holes so Im sure I can just throw these back on but as stated since Im at it I'd rather replacement if possible. Whats the time frame these should be replaced if any?

Any feedback on this would be great.
Thanks in advance.