Those faded buttons fool everyone, even me. I should send a bug report to Inkscape, as I already have one there now.
Maybe try a minimal disturb method
IN XML Editor if you click on a text node of a text that works.
Press the duplicate button
Open it's tree to the last line that shows the actual text and click on it.
Type the new text in the right pane, it's instantaneous
Go back up to the primary text node in the tree and click on font size.
In bottom right pane change it and press set.
EDIT
Well that's annoying.
It worked for one part, but text doesn't work in this new part.
I get the error when loading the svg in FZ saying that the fonts will be converted, and when it does it turns tiny.
From memory the other part didn't have the conversion error, and was fine.
EDIT EDIT
So I copy my text from the DENSO
Rotate -90º
Go in to XML Editor and change the label to MPX
Save and load.
Now the text doesn't error or shrink, but somehow the full part name is substituted instead of the MPX text 