Well, the thing that aligns the coupler is the T-bar that holds the coupler. The spring applies tension to the groove in the coupler shank and centers the coupler.
I've found that changing the t-bar and if it's the metal one, you can smooth it's legs, may help the coupler center better.
There are also the couplers that have the small centering spring and not the T-Bar arrangement. Those usually center, but the springs are somewhat fragile. Also, any friction in the back-n-forth movement of the coupler will cause it not to center properly every time, so some dry lube on the shank and washers may help.
