Gear Linkage Gaiter
At the rear end of the gear change cables there are concertina type boot gaiters. Unfortunately they have a tendency to degrade and fall apart, and because they are an integral part of the cable itself, it is not possible to purchase them individually from Rover - you have to buy the complete cable, and then struggle to fit the whole thing!

However, a length of bicycle inner-tube and a couple of tie-wraps will make an adequate replacement.

This is the Mark I version
Click to enlarge
Full acknowledgement to Dieter Koennecke for his original idea.

Unfortunately, it only lasted 6 months, probably due to the fact that it was being compressed severely every time I changed up a gear into 2nd or 4th. The new Mark II has been made of a much shorter length of inner-tube, with the rear most end being tie-wrapped to the white nylon sleeving of the cable itself. Since this sleeving does not move, the gaiter should last much longer.

This is the Mark II version
Click to enlarge