'87 740 Turbo sedan, 4 speed manual with push-button OD

In the summer my OD works flawlessly. In the winter when it is cold,it will not work until I have driven for a while. Here are the symptoms as I drive from cold start :

Kilometer 0-4
- When cold, and driving in the first few kilometers, pushing the OD button (While in 4th) does nothing at all...no engage, no light on dash, nothing

Kilometer 4-5
- Pushing button engages OD and turns dash light on but will auto disengage after a few seconds
- as I drive a more and more it will stay engaged longer and longer before disengaging

Kilometer 5 -8
- Pushing button engages OD and turns dash light on
- seems very sensitive...if I rap on the shifter it will disengage

Kilometer 8 and on....
- Everything works great, OD stays engaged and will not disengage unless I push the button

Does this have something to do with the temperature of the tranny fluid???
I have dismantled the shifter knob and made sure the connections are tight on a previous occasion.
Is this maybe a problem with solder joints on the relay?

Any ideas would be great.

Thanks in advance
Matt