wazzbat, the simple method that I use to try to estimate the remaining life of a reel is to look at how far the blades extend above the top of the lateral plates they are welded to. If the reel has never been reground, this is likely to be quite a bit - I haven't measured it, but at a guess, something like 10 mm. If it is only 3 mm, I'd suggest you keep looking: there is not enough remaining life in the reel, but generally, the more remaining "meat" the better. It seems to me that the majority of the SB45s that come up for sale in the eastern states have never been reground.
Of course you do not buy an SB45 just because its reel has say 8 mm of sharpening remaining. It might have bent blades, or worse, deep nicks in the blades from hitting foreign objects while mowing. It might also be distorted, perhaps due to some disaster that has twisted the reel out of shape so its axle is no longer perfectly straight. The mower might have a damaged frame, or something bad might have happened to the soleplate. The engine might be terminally ill. The identification plate might be missing, destroying the collector value. The clutch might be damaged. If the mower has done much work (which I think most eastern states ones have not) the chains and sprockets will probably be worn.
