"C J Campbell" wrote
The Cessna 172RG is similar.

All the Cessna retract singles have the same basic gear design. Only
difference is some of the earlier 210's had an engine driven hydraulic
pump.

Hydraulic pressure is used to hold the gear up. The pump runs every few
minutes to maintain hydraulic pressure.

If the pump is running every few minutes, there's a leak somewhere.

You would have to spring a leak at the bottom of the
sump to lose all your hydraulic fluid.

That's absolutely not correct. All you have to do is blow a high
pressure hose and you will pump all the hydraulic fluid overboard, and
completely lose any ability to lower the gear. Know more than one
person who has had it happen.

Michael