M103 is very stout, unless it was run cold all the time I doubt its worn out. Also test it on first gear start.
at a stop foot on brake, shift all the way down then back to D and go full throttle - the car will be in first gear, if you gingerly ease the throttle with lever in D shifted from P - the car will always start in 2nd gear (it was a feature to smooth the power delivery and prevent wheelspin)
If you are facing oil burn issues - then the most probable cause is worn valve guide seals (common on this engine at high miles) - this engine will also blow its headgasket at high miles due to the dissimilar metal sandwich between the head n block (its not very expensive either - just find a good technician/mechanic to repair it right, seal the upper timing cover with hylomar and use a socket to prestretch the cam oil seal first.
use caltex delo gold oil in this engine - its proven to be the best for me.