My BIL has a circulator pump leaking around the shaft into the motor.
Is replacing the seal on a B&G LR20 as straightforward as it seems?

Disconnect wires, remove pump, remove impeller, pry off ceramic seal,
replace shaft seal

Can I trust the flo-control valves to keep the system from draining?

The furnace is in the basement and all of the pumps and valves are
mounted high near the ceiling. There are shutoff valves for each zone
on the return side and flo-control vavles after each pump on the supply
side. No shutoff valves for the pumps and I would like to avoid
draining the whole system of a split level house with three zones.