Take the lens caps ff.Then run a new Leupold under it..

If this is one of the old 600 model series from Japan, and it has a BDC option (dual horizontal crosshairs), the threads may be stripped on the plastic cap or sleeve that engages the elevation screw (common problem). The cap may also be cracked. You may have to be on the lookout (ebay, gunbroker, etc.) for a replacement cap. In the meantime, you can just remove the plastic cap and use a screwdriver to turn the metal screw on the scope body under that cap to adjust elevation. If this does not solve the problem, there is a scope repair shop that specializes in repairing vintage scopes (Ross, Ohio). This work would be beyond the "scope" of an amateur. Hope this helps. erik7x57