Build 39.67.5
noticed on Multiplayer (Steam dedicated server, 2 players, no Mods)
reproduced on singleplayer.
I don't know if it is just a visual bug, or actually affecting repair %, but leveling Metalworking and Mechanics can decreases the displayed "Potentially Repairs %" on the vehicle UI.
I noticed this with my MP character when my repair % dropped from 61% to 47% going from Metalworker 3 to 4 (Mechanic lv10). The same seems to happen from Mechanic 2 to 3 as well.
Leveling both to 10 grants 55% repair which is still less than the 61% from lower levels.
Single Player reproduction below:
3 MW, 2 Mechanic - 61%
3MW, 3 Mechanic - 52%
3 MW, 10 Mechanic - 61% again
4 MW, 10 Mechanic - 47%
10 MW, 10 Mechanic - 55%