337D : Gear extension took "forever" out of Annual

[AV8ing]

Aviators : First flight following the Annual Inspection, 1965 337D Model, the gear retracted normally but the extension took way too long.
I didn't time it but I'd say it was pretty close to a minute.
No other anomalies noted.
I should add that the left rear main gear door actuator was opened up to repair a small leak, and the hydraulic reservoir was replenished before flight.

Any ideas what may have caused this ?