I agree with OWD on this. A lever that drifts left normally means the bolt has a taper & as the locking surface of either the bolt or the lug's bite bite wear, the bolt enters deeper so the lever goes left. I have three guns in my cabinet on which the lever always stops at center. One an early Lefever has a bolt adjuster which is not connected to the top lever.
On the other two there is no bolt wear compensation built in at all. The bolting surfaces are simply parallel. Yet both of these guns though over 100 years old & shoe use, but not abuse, bolt up tightly. If you close the gun fully & firmly, but not so hard that the barrel tends to bounce, the bolt simply snaps home with virtually no contact to the lug's bite, thus no wear. "IF" on the other hand you close the barrels very gently & ease the bolt home it rubs all the way to its seat, thus creating friction which promotes wear.
Pure Mechanics.
