The 103 motor does have a tendency to use oil through the valve guide oil seals. I wouldn't worry about it if the consumption was less than a quart evey 1000 miles.
The subsequent formation of carbon has caused some amount of idle problems. As your tech pointed out, vacuum leaks can cause single cylinder lean misfires. Check the archives for vacuum leak diagnostic techniques.
Bosch Master, ASE Master, L1
33 years MB technician