You may have two or more problems manifesting themselves.

Failure to engage until warm may be the 4th gear switch which would also contribute to the intermittant operation once warmed up.

There is a built in delay in the relay after you push the button or shift out of gear to disengage the OD before it allows re-engagement. It is about two seconds. This is to protect the sliding member from getting conflicting torque applications during its "in between" states. Similar to damage done if OD is stuck on and in reverse then releases while moving.

The funcky engagement might be a gummed up solenoid, poor electrical connections, the 4th gear switch reacting to engine torque as the shift lever flops around, low fluid, or poor actuating piston seals that get worse as the OD warms up.

I'll send you a electrical trouble shooting guide to eliminate the electrical problems. After that it may be time for some new seals.

Duane