Gear doors not closing on gear extension.

[B2C2]

I had this issue as well when I first bought my T337D skymaster. The switches would close on the ground after following the manual procedure for setup but not in the air. The issue is that the airflow over the back of the plane in flight creates negative pressure that forces the gear away from the switches. If these don't all close the gear doors won't close either. A slightly more aggressive adjustment on the switch position fixed the problem. I haven't had it since. One other issue I have consistently is that the hydraulic mule used to swing the gear on the ground would suck hydraulic fluid out on shutdown. So every year I remind the A&P to top up the fluid after annual.