After a lot of time, we have just found a good solution to repair your scratched HP41C screen. There is an abrasive product used to repair watches' plastic screens, called Poliwatch. You can easily get it from Amazon and other sources.
Here is the link to the product in Amazon (click on the picture):
The method: just apply a little quantity on the scratch, and then rub firmly with a soft cloth. You will get, once cleaned, a bright surface without scratches. Note: after some tests, we have found that the dremel method can overheat the plastic and lead to internal cracks or material deformation. It has to be manual!
Beware: do not try to use this material on crystal - it is so hard that it would not help at all.