Summasketch III digitizer repair

[cvbt-thailand]

We have a digitizer we are trying to resurrect:

SummaSketch III with 4-button Diamond Puck
12 x 12 MM compatible version 1.91
Win XP SP2 (version 5.01 build 2600)
Tablet Works 7.46.0619
com1

All buttons work and are assignable
The puck works in mouse mode.
In WYPIWYG mode there seems to be some problem:
In Tablet Works Control Panel, the digitizer area doesn't stick - the (almost) whole digitizer area is still used; a small selectable area cannot be defined.

I use this in AutoCAD with the Wintab Comaptible Digitizer ADI 4.2 - by AutoDesk.
AutoCAD will recognize the tablet and allow me to configure regions and a screen pointing area. Menu items on the tablet work and the screen area allows geometry selection.

Here's the problem (you could feel it coming couldn't you):

Counting up from the lower left corner of the tablet
The tablet "sees" (steady indicator light)
from about (4.75cm, 4.3cm) (my ref: X-5)
to (28.0cm, 26.5cm) (my ref: B-27)

The problem is It should see the whole tablet area but it doesn't.

In the GTCO tablet configuration utilities the cursor can paint the test screen area from the lower left corner to about 75% of the test screen area up and to the right.

A few years ago we had a problem with the puck: A button wasn't working. We repaired it. The cross-hairs cover fell out and the coil wire broke, we resoldered it. I don't remember clearly but we may have tried to replace some of the coil wire.

Questions:
How can I repair this here myself?
If the coil is not the correct sensitivity will that cause the symptoms we have?
What is the correct wire size and number of turns for the coil?
Any suggestions on how to rewind it?
The felt on the bottom of the puck is worn. Do you have a suggestion for a replacement material?
What is a good way to keep the cross-hairs cover from falling out?

We are a not-for-profit NGO that works to help rural villagers have good empolyment by making building materials on a small scale. We use AutoCAD to design buildings that use their materials and equipment and tools for them to produce the materials. We also mentor interns from local and foreign universities and colleges.

We would appreciate any help you can give us.