Hi Derek
I have had to make some replacement sheets in the past and they do work very well. The photo below shows the damaged original from a Beomaster 2400 and a paper print of one that I drew up in AutoCad. Thereafter, all I had to do was print it out on to transparency paper and cut it to size. Everything fitted and works nicely.
I think that this print will become damaged over time especially if the tone changes and balance changes are frequent. However, I make very few adjustments to these parameters so everything continues to look good. In any case, the final print onto the transparency always makes six of these plastic sheets so I do have plenty of spares.
From memory, the plastic sheets on the BM1900 are a bit simpler with less lines and more solid blocks.
Have fun
Geoff