Although people complain a lot about Lucas electricals, I've found that all the switches and lamp sockets I've had trouble with can be taken apart and cleaned. I don't specifically remember about the light switch but take a look and see if it doesn't have small metal tabs that can be bent out and the plastic part removed to access the insides for service. I don't think I had to replace any of the switches but I know I opened several up for cleaning. I also had good luck with servicing the lamp holders used in the gauges. I don't think they open up but contact cleaner and some cleaning fixed them up.
Here's an update on Larry's switch suggestion.... as of early 2014, this is still a good P/N. Switch is an excellent choice for a replacement. And just as a point of documentation, the original chrome rosette fits this switch, and tapping the original knob as Larry suggested (10-32 threads) gives an original look.