I own a Weston Master 5 (newer than yours I know) and have found it to be an exceptionally reliable bit of kit. I purchased mine secondhand from the original owner and although it has never been checked or repaired it still works as well as the day it rolled off the production line.
I know that compared to some of todays modern meters at £300 a pop my little WM is kinda basic but I wouldn't change it for the world.
The Master series use selenium cells, I'm told they're sensitive to damp. I have a Master III and I try to keep it in a dry environment or (barring that) in a warm pocket. They work, they're relatively inexpensive, and they're pretty!