Hi . I've just bought a used Zuiko OM 35-70mm f3.6 lens on eBay. It seems in pretty good condition throughout except the zoom ring which is quite stiff, especially towards the wide-angle setting end. Is this likely to be an expensive repair, or just something like lubrication of bearings? The seller said all the mechanisms were smooth and free. Seller has 100% pos. feedback so maybe they weren't fully aware of this issue? Thanks for any advice. John.