I actually considered and would of done the same as you with the packing tape.Except i dont trust my tubes integrity being only approxiamately .7 mm thick for almost half of its diameter.And the stuffing around of sanding a dowel to fit did'nt appeal when i thought obtaining a replacement would be easier and fix all the problems with it.Except,getting hold of the replacement is proving harder than i imagined !.

Performance Metals Australia replied back to me this morning and can provide what i need in the recommended grade of 6061-T6 and will post direct to me,and,for a very good price.Actually less than the cost of postage.Thanks fellas.
Once installed i'll have piece of mind in that area.