Since the springs are Ok either the cylinder is binding or there is something restricting the return flow of oil. A good hydraulic shop should be able to rebuild the cylinder without much of a problem. The next potential problem I'm wondering if you have a sticking valve that is restricting the flow of oil back to the valve block. Been a while since I last helped out the missile launcher techs on my last ship so my hydraulic theory is a bit rusty.
2006 Hurricane 31D aka 'Moby' the Whale
FCC(SW) US Navy Retired 1980-2003
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If you are swapping a old style spring with another old style spring you haven't learned much. The new style springs are stronger. You can identify the new ones by the shape of the coils on the ends. They are wound with a taper like a bee hive at the ends. The old style all the coils all the way to the ends are the same diameter.
Get a set of new style springs from HWH and a can of spray silicone and try again.