Michael, I am not at all surprised that yours uses the same gear pump as mine, but I don’t know how those pumps work internally. Looking at the website I think they are just standard gear pumps i.e. 2 gears meshing together, with various valves added according to how you build the P/N from the various options (for typical landing gear usage you want the pump to be fully blocking in both directions so when the motor stops the fluid cannot flow back).
I doubt you can inspect the internals without a full dismantling. You could try obtaining the overhaul manual for the pump; it might need some subterfuge 
OTOH I think the non return valves are just things which screw in from the outside so they might be removable individually.
You will definitely need to bleed the system and that’s worth doing anyway, to get fresh fluid in there.
Are you sure the leak is in the pump? It could be in the emergency gear release valve (if you have one) – that’s a classic leakage point. Or in one of the hydraulic actuators.
Usually this type of gear is held up by hydraulic pressure only. If the pressure drops a pressure sensing switch will activate the pump. If the gear starts to drop in flight that would indicate that the pump has not started, perhaps a faulty pressure switch or a sticking relay. If there is a leak past a seal in the system (most likely an actuator or the emergency gear release) this can cause the pump to operate very often in flight as the pressure drops. This in turn can weaken or burn the “up” relay, making it intermittent. Therefore I think there are potentially two problems: a leaking seal and intermittent electrics.
LeSving wrote:
The Carbon Cub cannot run on other fuel than 100LL for instance.
Not according to the website.
This in turn can weaken or burn the “up” relay, making it intermittent.
That failure should be evident from the gear gradually dropping and the pump not running. The system is fairly easy to troubleshoot with a voltmeter. If the gear is dropping and there is voltage across the pressure switch, then the switch is faulty. Same with the up relay contact.
Squat switches can make it more complicated, but they aren’t relevant when the gear is up (or supposed to be up) and anyway AIUI not all homebuilts/ULs have squats (some have an airspeed interlock, or nothing).
I had presumed that the pump was not running when the gear dropped in flight. If the gear dropped in spite of the pump running this would mean a major internal leak which would be unlikely to be intermittent. The fault is most likely electrical, especially after it recurred after a winter lay up. Slight corrosion in contacts perhaps?
Since we are at it again.
Peter wrote:
The cable also needs to be adjusted so that it is “stressed” (compressed, and thus buckling slightly) when the red knob is fully pushed in. That ensures the valve is closed and remains closed
Yep, that was the gear trouble this week. Not finally resolved (will need a permanent solution springy or rubbery) but fixed.
After new pressure switch and new rubber seals in the emergency release valve, i have had my fair share of gear probs.
