Simple questions first. First and reverse engagement problems most likey related to a need for clutch cable adjustment.

OD not engaging until after its warm. Does the dash light not turn on when this does not happen? Next time it does not turn on, pull the shift lever to the rear and to the right more and try again. If shifts into OD then, replace 4th gear switch on right side of tranny.

Dash light turns on but not the OD? Wires to and from the solenoid on the left side of the OD need cleaning and tightening.

The hard one. Clicky OD. It just wants to be with the in crowd???
This is one where I wish I could hear it. So many words to describe the sound and each means something different to each individual.

Rapid or slow relative to speed. Muted or sharp. Metronomic or rythmic.

In OD mode, two more components rotate and one stops rotating than when in gear mode. Since the noise is only in OD mode this eliminates the three support bearings, leaving the planetary gear cluster and the Sprague clutch as the new rotating components.

It would be best to take the OD apart and see the problem. Trouble with taking it apart is the down time of the vehicle and in the worse case, the part needed is not available or cannot be found in salvage.

Combining sounds is the next best and may lead to a direction to facilitate repair.

Slow, muted and rhythmic. Points to the planetary system. That is not available as a new repair part so look to salvage yard or rebuilt OD. Rebuild the salvage yard before install.

Rapid, sharp, metronomic. Points to the Sprague clutch. Either the cage is hanging a roller or the components are binding and the clicking could be from the thrust washer.

A method to isolate which may not be diffinitive. Listen to the OD while under the car and OD engaged. Stunt Actors Guild licence not required if you remove the drive shaft and stay away from the rotating flange with your body and clothing.

Using a stethoscope or similar trick, if the noise is louder from the front, it is the planetary system, if from the rear it is the Sprague system.

Repair and cost. Planetary system. The best deal you can make from the salvage yard and refurbish components cost. Gaskets and seals, etc.

Sprague system. Depends. Complete Sprague assemble plus thrust washer would run in the neighborhood of $155 from my supplier. Thrust washer alone $30. Individual components less accordingly.

Most likely a salvage yard unit would be cheaper if from a U-Pull-It type yard even with a refurbish kit. From a regular yard I'm not sure.

Suggestion. Since in the worse case in each instance above, the cost to repair would seem to exceed the cost of a unit from a salvage yard plus refurbish kit, go the salvage route. Look for any 240 or 700 series from 81 to 86 that has body damage. Preferably not direct frontal that contacted the motor or rear end. Those crashes tend to stress drive train components in the worst possible way.

One other trick I have heard of being used is to turn up the radio until the noise goes away. Works well on those vehicles that can be left at the side of the road without worry! Makes for difficult conversation though.

Duane