By Andrew Fawkes, (Reproduced from a forum post)

Whilst replacing the springs in the wiper arms does improve things, it wasn't a perfect result for one arm (weirdly). Also, I'm aware that inferior rubber is being used in modern wiper blades so that they jump/bounce across the screen rather than sliding smoothly to clear water.

Here's how to replace the blade rubber with modern (silicon-based) blades... or at least how I did it.
1. Remove the blade with its metal case from the wiper arm then remove the rubber blade. It slides out in one direction:
 

2. I bought Bosch blades from Halfords that were the same length (15") as those on my DB6.
Slim-nosed pliers easily bent back the tabs to remove the rubber blade complete with its metal support.

3. Slide the rubber off the metal supports (thus leaving behind two slim metal rods):

 
4. Feed the new rubber blade into the groove on your 'old' wiper arm. There is a wider angled opening at one end to facilitate this:
 
Trim the leading end so that the grooves on each side extend to the end of the rubber. This enables the new blade to fit snugly along its whole length:

 
The new blade will now work well when replaced on the car... or at least it did in my case!

 
Note: If elite concours is your thing, you might want to retain a pair of the 'old style' blades for fitting prior to judging. If you're anything like me, you will have collected a few spare blades over the years in an effort to find some that wipe properly... like these Bosch ones now do!

Good luck.