Andy replies:

Carl's suggestion is a good one. A cylinder can be hydrolocked
from any liquid that gets into it and fills it. Usually that is OIL.
Taking out the plug and pulling it thru a couple times fixes this,
or at least identifies the problem....

However, if the blade turns, the system is not hydrolocked, UNLESS
the blade is turned by a belt, and the belt is slipping...... In a
simple
little rotary mower, there is no belt....hence, no hydrolock...

Andy in Eureka, Texas