I just finished a messy and protracted job of hunting down and fixing an
internal hydraulic leak on my 360.  The system would hold pressure for only a
few minutes on the ground before the pump would cycle.  In the air it was
about a half hour.  Having reached this far down the squawk list of
annoyances, I decided it was time to put the plane on jacks and finally fix
this.

I have hydraulic pressure gages on the panel so I decided to progressively
remove components until the pressure stabilized.  I would fix the offending
component and declare victory.  Not so simple.  As I removed parts and capped
off the lines, I could see improvement but not complete satisfaction.
Finally, I had nothing but the pump and the gages in the circuit and decided
that pressure was holding so I declared the pump OK.  Next I decided to go
ahead and rebuild the nose gear cylinder and it's door cylinder since I judged
these suspects from the preceding tests.  The nose gear cylinder required a
call to the Aero-Tek factory to figure out how to get it apart.  Hint:  remove
the 90 degree elbow fittings first.  When I inspected the cylinder inside wall
I discovered significant scoring and metal grit around the O-rings.  I had
found my smoking gun.  The scoring was worse where the piston sits in gear
down.  Makes sense as this is where particles might collect.  I got new
cylinder tubes from Aero-tek for about one third of the cost of new assemblies
and reassembled everything.  I decided that the main gear cylinders should
receive identical treatment and these proved to be scored too but less so.  I
also removed the pump and cleaned out the reservoir.  There was a lot of black
soot at the bottom which I'm certain was telltale of my problems.

Hydraulic pressure (about half) now remains even over night which is plenty.
This system finally behaves itself.  The moral of this story is that I needed
to be far more sanitary during construction to keep the grit out of the
system.  The Aero-Tek engineer said the fiberglass grit really eats them up.
And don't reuse fluid.  I tried to economize by running used fluid back
through a paper towel filter.  This is just dumb and not worth the small
savings since the black soot doesn't get filtered out.

Ed de Chazal
N361DC