Hi Ian,

I've got pressure gages on my panel and have seen the same thing regarding
pressure bleed.  I overhauled the cylinders and discovered that several tubes
had scored walls, allowing fluid to seep by.   I got new tubes from the
manufacturer ($50 instead of $150 for all new assemblies) and the problem is
greatly improved.  My theory as to why this is worse in the gear extended
situation is that this is where the gear spends most its time and hence bits
of debris in the system collects at this point in the nose gear.   Repeated
cycling of the gear with debris inside the hydraulics causes scrapes.  Check
your nose gear first.

This is important because what happens in summer is that the fluid leaks
across into the low pressure side, the pump for some reason does not allow
this pressure to vent to the reservoir.  Then, while you taxi to the active,
the system heats up causing pressure in both circuits to rise together.  If
this pressure rises to 800 psi, the switches will not allow you to raise the
landing gear and actuating the dump valve will have no effect.  You will be
stuck until you land and crack the system to let pressure out.  I know because
it has happened to me several times until I started pulling the breaker on the
ground.  With overhauled cylinders, it's no longer a threat.

Good Luck,
Ed de Chazal