I'm looking at a Yashica Mat 124G camera for $200 (auction site). Seller claims pristine condition and very recent CLA (seals were replaced). One flaw that he mentions is that the fastest shutter speeds are off by a stop -- e.g. 1/500 clocks at 1/250, etc. As I occasionally shoot fast moving subjects, this is a concern. But on the other hand, maybe most of these cameras develop this problem as they age (does anyone know?), and I'd have been none the wiser otherwise.

So I'm wondering: How extensive a repair is this? Is it something I can do myself (probably not)? Should I just keep shopping? Or just not worry about it?