The whole thing removes from the bus quite easily, just be very careful when dismantling

A good clean inside and out will make quite a difference and you can access the remaining inner area. A simple bottle cleaning brush will clean out the detritus and dust quite nicely.

On the one I did, the silvering on the glass mirror had gone.
A local glazier cut me some replacements to the same size. But metric standards meant that the glass being thicker. In hindsight, thinner than original would be better (if they have it) as these can be packed to fit tight and rattle free with glaziers tape.

This made it a little harder to refit, but done with a bit of very careful tweaking.

What was missing were the sightlines. These were etched on the original glass. I simply used Letraset graphic lining tape to replicate. It's worked fine.

The housing was easy to strip clean and repaint off the bus and the spring easy to replace. I went online and bought an identical type by using the old one as a size guide .

When repainting it is best to use an absolute flat matt black inside. The less stray light and reflection, the better the ultimate image, any sheen or shine affects the view.

Also, when reassembling, a very thin smear of non-setting mastic used as a seal will keep out dust and moisture. Has to be done at both ends and in dry conditions.

When done it really made a difference with a clear and easy view of the blind.

http://www.leespring.co.uk/uk_torsion_spec.asp?springType=T&forWhat=Search