Recently my '89 240 has started showing her true personality...from phantom rising temperature gauge to the more annoying trend of not shifting into overdrive!

As the overdrive has an affect on my 80 mile daily commute, I need to do something about it! It isn't always that she screams in 3rd gear on the freeway, just intermittently. It appears more pronounced when the vehicle is fist driven. Once it shifts into OD (when it does) it seems that even after stopping, it shifts fine...it's the initial reminder that it needs!

I have heard of a solenoid on the top of the transmission that sometimes gets plugged up or fails. I have also heard of the nightmares of removing it with some hand made bent up wrench! Someone even mentioned to me that I can use a dremel tool to cut a path in it between two sids that will make it constantly shift into OD.

Can any of you Brick Gurus offer any suggestions:
Is there anything but the solenoid that could be causing this problem? What and where is it located?
How hard is it to replace?
How Expensive is it?
What tooling is required to do it on my back under the car?
Can the existing unit be "cut" to allow constant acceptance into OD? How do you do it?

Any help would be greatly appreciated.

Regards,
Rob