I had originally thought that this plastic was a small piece.  My plan was to simply replace it entirely.  However, when I disassembled the top of the playfield, I realized that this plastic was very large, and spanned the ball lock.  Since it is not practical for me to build such a large piece, and I did not want to cut the plastic in half, I had little choice but to just replace the small part that was missing.

I found a scan of this plastic on ballsofsteel.net.  I cleaned up the image by removing blemishes and making the colors solid.  I then printed the first test print on glossy photo paper with a color wheel.  That allowed me to calibrate and color match.  The next important part is to figure out what to print on.  I tried a variety of substrates (waterslide paper, clear transparency plastic, translucent paper, glossy photo paper, etc).  I needed to match the translucence of the original plastic (when backlit), and also how it looks under ambient light (front lit).  In the end I found that, surprisingly, ordinary white paper produced the best look.  Thicker paper blocked too much light, and painting a clear film white produced too many brush strokes or also blocked too much light.

So the color-corrected image was simply printed on plain white paper, and then bonded on some polished cut Lexan plastic.  The glue used was 467MP transfer adhesive (sample courtesy of Bryan Kelly) .  The results were very good.  When backlite (above image), the amount of light blocking matched quite closely with the original plastic.  Also, when lit with ambient light such as from the GI circuits, the match was very close.  Be sure to rub down firmly to remove the tiny air bubbles under the glue.

The original plastic was trimmed back to a black line, and the new piece was mounted with a clear protector underneath.  In addition to preventing ball hits, this protector also serves as a means to line up the original plastic with the new one.

Ramp Repair

Another commonly broken part on this machine is the mounting tab of the ramp.  Since it is exposed, ball hits tend to break this tab off.

The tab was repaired by cutting out a small piece of clear Lexan.  The bottom of the existing tab and the new piece were sanded rough.  These were then cleaned with alcohol.  Then the new tab was epoxied under the existing tab.  I then prepared a tape dam all the way around the tab and dripped in more epoxy to replace the missing plastic.  This technique produced a flat square edge, matching the original ramp's appearance.  After it is all cured, the ramp was test fitted into the machine, and the mounting hole marked and drilled while the tab is still transparent.  Finally, the top face of the tab is sanded flat, and painted with acrylic paint.  I found a color among my collection that matches the color of the ramp very closely.  It is "Folk Art # 719 Plaid Blue Ribbon".

Ball lock repair
The two ball locks in the back of the playfield performed poorly mainly due to damage at their entrance.  To begin with, hard shots from the flippers would very often cause frustrating bounce-outs.  In addition, once a ball was locked, the depression in the playfield cause by the wear would sometimes trap a second ball, and you had to nudge the machine to get the ball out.  Finally, the ball eject mechanisms would sometimes get stuck in the 'up' position, and it would not allow the ball to enter the lock.