@Paul Howell -- don't spend much money on a Leicaflex - oldest or SL variety. It's one of those things that may be working fine when you get it and stop working relatively quickly. Getting them fixed seems to be a challenge.
Prices people mention here are very high in my experience..... I bought several SL's and lenses over the past couple of years, paying typically some €200 - €270 for an SL in good shape including Summicron 50 lens, sold some for similar prices
Like many high precision mechanical devices, being left on a collectors' shelf to be gloated about is about the worst possible thing that can happen to them.