any one with experience, I have a 1970 2520 I just picked up and the rockshaft drops all the way down within an hour under no load......ideas???---thanks!
Pretty common for older machines to have a bad lift piston seal. If there is a flow control valve (drop speed) try closing it all the way with the lift up. If it still drops your lift seal is probably going bad. Mine did that for a few years before I replaced the seal and honed the cylinder. It was a non issue until it began oscillating in use.
Could be faulty RS piston seal,leaking control valves Or leaking thermal relief valve. You could try as Fawken suggested to tighten down rate of drop screw(parts key 8)