How does the OD engage once it makes the attempt? Taking about 1/2 second, which is normal, or longer with some slipping and "chatter" as it tries to lock up?

Low fluid usually does not take the delay time engagement scenario. Low fluid usually tries from the start to engage with chatter and slippage then over time not engage at all due to air getting beat into the fluid.

A delay like you indicate is more likely to be a sticky 4th gear switch, bad or dirty electrical connection, or dirty solenoid.

If the delay gets less as the vehicle warms up, 4th gear switch. Get longer as the vehicle warms up, solenoid, with a no disengagemnt problem showing up later. Random times electrical connections.

If the actuating piston O-rings are just failing, the symptom you describe will occur within a specific time delay. There may or may not be slippage or "chatter" as the OD engages.

I'd guess the 4th gear switch at this time.

Duane

P.S. Once this unit is out to make the change to the Amazon, refurbish the actuating piston O-rings and the solenoid before you install. A lot easier with the unit on the floor than from underneath.