According to Monte's installation instructions there is a warning about differing revisions on the LCD display. Revision F LCD panels need an installation of a .01uF (10nF) from the OS1 pin out on the keyboard pca pinout. The ground is pin two of the keyboard logic pca. These two pins can be found at the LCD pinouts at the top of the keyboard pca also (figure 2). This LCD pinout would be the easiest area to attach the 0.01uF capacitor.
Internally the full nut early HP 41C that have the plastic capped display drivers (figure 1) are the ones that need the capacitor modification seen below.
The modification entails the addition of a capacitor to the location indicated in figure 2.